Section III—Muscular System

Muscle Terminology

Tables 7.2 to 7.4 list the muscles covered here, includ­ing their areas of origin, insertion, and main actions. Muscles may be named according to several criteria.

Connective Tissue and Fiber Direction

Various features and structures are associated with the muscles, but dissection and identification of the muscles requires knowing only the following features. When the skin has been removed, you will note that the muscles are covered by connective tissue. There are various kinds of connective tissue: epimysium covers or envelops the surface of individual muscles; loose con­nective tissue lies between structures (such as muscles, nerves, or blood vessels) and helps fill the spaces between them; fascia is a very dense, sheet-like connec­tive tissue associated in various ways with muscles; and tendons are dense connective tissue that connect muscles (mainly) to skeletal elements.

The visible fibers of a muscle will all tend, in the major­ity of cases, to have a similar direction. It is very helpful to note fiber direction in distinguishing where one muscle ends and another begins, particularly when muscles overlap one another. This is an important clue in identifying muscles, as well as in knowing where to separate them.

Fiber direction, however, is often obscured by connec­tive tissue, and thus it is essential that you remove the connective tissue until the direction is clearly revealed.

loose connective tissue

tendon

You do not need to clean the whole surface of every muscle. It is sufficient to clear surfaces near where text directions indicate the edges of muscles should be. Most connective tissue can usually be picked away using forceps and a dissecting needle. It is sometimes, but rarely, necessary to use a scalpel in nicking away the connective tissue on the surface of a muscle. Separating muscles can usually be accomplished by using a blunt probe to tear through loose connective tissue. A scalpel should not (unless indicated) be used to cut between muscles. In clearing connective tissue, then, you will be mainly concerned with epimysium or loose connective tissue. You will not cut through aponeuroses or fascia, unless specifically directed to do so.

Key Terms: Muscular System

aponeurosis epimysium fascia

subdivision of the Musculature

As for the dogfish, the musculature of the cat may be subdivided into formal groups based on phylogenetic derivation. The major muscles can be identified to group based on embryology and innervation. However, the muscles of the cat have undergone considerable modifi­cation and are much more complex than in the dogfish. Thus, the musculature from any formal group usually cannot be studied at the same time, because some muscles lie superficially and others more deeply.

Skinning the Cat

To examine the muscles and other internal structures, the cat will have to be skinned, but the skin should not be completely removed. It is best to remove the skin from only part of the cat and leave it as a flap that can be wrapped around the cat at the end of each dissec­tion. This helps protect the muscles and other structures and prolongs preservation of your specimen.

Before beginning, read the instructions below with your specimen in front of you, and assess where you will cut through the skin. Determine the course of the incisions according to these instructions and Figure 7.26. Once skinning is completed, you will have a flap of skin still

155

TABLE 7.3 Muscles of the hind limb

FIGURE 7.26 Diagrams showing incision lines to be followed in skinning the cat.

attached ventrally on one side of the chest, abdomen, and groin. For example, if your first longitudinal inci­sion is on the right side of the middorsal line, then you will skin mainly the left side of the body, skinning the left arm and leg, and leaving the skin attached on the right side of the ventral surface of the cat. It does not matter which side of the body you choose to skin. However, avoid skinning a side if it has been damaged or had skin removed to facilitate injection of vessels. For example, in most specimens the skin on one side of the throat will probably have been removed and the musculature damaged when the arteries and veins were injected. Sometimes, an area in the abdomen will have been skinned and cut to inject the hepatic portal system.

You need not make all the incisions before you begin skinning. Using a new scalpel blade, make a shallow longitudinal incision along the back, about 1 cm to one side of the neural processes of the vertebrae. As you cut, ensure that you have cut only through the skin by reflecting the edge of the flap. Extend the cut from near the base of the tail forward onto the back, neck, and head past the pinnae. At about the level of the eyes, make a sideways incision toward the other side eye (that is, cut back across and past the middorsal line), angling the incision toward the back of the eye. Continue to cut toward the back of the mouth and onto the underside of the lower jaw. Follow around the mandible to the other side. Return to the base of the tail and extend the incision back across the midline, around and under the tail. Continue forward, anterior to and then around the external genitalia. Continue the incision to just past the midventral line. Make an encircling cut around the forelimb, about midway along the antebrachium. Do the same for the hind limb, just past the ankle. Then make another incision, on the lateral surface of the hind limb, between this encircling incision and the longitudi­nal incision on the back.

Skinning can be accomplished by various techniques. For much of the back, for example, the skin is often readily removed, and a blunt probe, forceps, or your fingers will do the job of tearing through the fibrous connective tissue. In other areas, the skin adheres more strongly, and requires a scalpel. When using a scalpel, hold the blade parallel with the surface of the body and use short strokes; often, simply nicking the connective tissue will suffice, especially if you pull the skin flap away from the body to tense the connective tissue. You will encounter small nerves and blood vessels passing to the skin. Cut through them. As you skin the trunk, you will notice thin and narrow bands of muscles that adhere to the underside of the skin. These bundles rep­resent the cutaneous maximus, one of the cutaneous muscles, a large sheet that covers much of the trunk and is especially prominent ventrally and near the axilla (armpit). This muscle should be removed with the skin, except near the axilla. In this region, it adheres strongly to the shoulder muscles and should be cut.

In a pregnant or lactating female, the mammary glands (see page 217) will be large, flattened, glandular masses in the thoracic and abdominal regions, and should be removed with the skin. If your specimen is a male, be careful in skinning the groin region. A large wad of fat, which contains the spermatic cords (see page 216) that you will need to see later, lies beneath the skin in this region. Leave the wad of fat intact.

The skin on the neck and throat may be more difficult to remove. Dissect carefully so that you do not injure the vessels in the neck and throat. The skin of the head is very thick and difficult to remove. Use care so that you do not injure the various vessels, nerves, and ducts and the salivary glands that lie just below and beside the pinna. It is not worth trying to skin the pinna; simply cut through it, leaving a stump about 1 cm long. Another cutaneous muscle will be found over much of the head and neck.

In skinning the arm and leg, tear the connective tissue with a probe or forceps to separate the skin and muscles, but try not to tear the skin itself. Proceed from both the trunk down the limb as well as from the encircling cut up the limb. The skin may adhere closely to the muscles. Dissect especially carefully along the anterolateral surface of the brachium. The cephalic vein (see Figure 7.27) lies here and should not be removed with the skin.

Appendicular Musculature

Much of the musculature that you will dissect includes the appendicular muscles, i.e., those associated with the forelimb and hind limb. Thus, if either or both ends of a muscle attach to the scapula (or pelvis) or more distal limb element, it can be considered an appendicular muscle. These muscles will be organized into superficial and deep portions and will be observed with the cat positioned so as to give you lateral and ventral views of its body.

Muscles of the Forelimb

Table 7.2 lists the forelimb musculature and indicates their origin, insertion, and main functions.

Superficial Forelimb Muscles: Lateral View

(Figure 7.27)

Examine the cat in lateral view. Identify the large, white lumbodorsal fascia covering the back in the lumbar region. The fascia is actually composed of two main sheets of tough connective tissue, one above the other. The latissimus dorsi is the wide muscle that originates mainly from the lateral margin of the fascia. Its fibers pass anteroventrally and converge toward the axillary region. It pulls the humerus posterodorsally. The muscle emerging from under the latissimus dorsi and extending onto the abdomen is the external oblique (see below).

Anterior to the latissimus dorsi are three trapezius muscles. The most posterior is the triangular spino- trapezius, which draws the scapula posterodorsally. From their middorsal origin, the fibers of the spino- trapezius pass anteroventrally and converge toward the scapular spine. Next anteriorly is the acromiotrapezius. It is wider, but very thin. Its fibers fan out from their insertion along the scapular spine toward the middor­sal line, but do not extend all the way to the middorsal line. Instead, they attach to a thin aponeurosis. The acromiotrapezius can stabilize the scapula or pull it toward the dorsal midline. The most anterior trapezius muscle is the clavotrapezius, which covers most of the neck laterally and pulls the scapula anterodorsally. It is a wide muscle that originates from the neck middorsally, extending from just behind the skull to the acromio- trapezius. Its fibers pass almost directly ventrally toward the front of the shoulder. In mammals with a well- developed clavicle, the clavotrapezius inserts on the clavicle. As the clavicle is greatly reduced in the cat, however, the clavotrapezius inserts partly on the clavi­cle and partly onto another muscle, the clavobrachialis, which continues ventrally to insert on the ulna. Actu­ally, a raphe (a narrow band of collagen fibers to which muscle fibers may attach), as well as the clavicle, sepa­rates these muscles; as their fibers appear to be contin­uous across the raphe, they seem to form a single muscle. The clavicle is embedded in the musculature but may be discerned by palpation (see below).

The sternomastoid lies anterior to the clavotrapezius. It is not an appendicular muscle, but should be identified at this point. It extends from the mastoid process of the skull (see Section I), just posterior to the ear, along the anterior margin of the clavotrapezius, but then veers medially to insert on the sternum. The sternomastoid will be considered again below. For now, note the parotid and mandibular glands, also considered in detail later, that lie on its anterior part, and that the muscle is crossed by the large external jugular vein.

Examine the musculature of the shoulder and forelimb in lateral view. The cephalic vein lies on the anterolat­eral surface of the brachium. The spinodeltoid muscle extends anteroventrally from the scapular spine, arising at the insertion of the acromiotrapezius. Its anterior end passes deep to the triangular acromiodeltoid. These muscles are flexors and lateral rotators of the humerus. The narrow levator scapulae ventralis, lying dorsal to the acromiodeltoid, extends anterodorsally and then passes deep to the posterior margin of the clavotrape- zius. The long head of the triceps brachii covers the brachium posteriorly, while the lateral head of the triceps covers the brachium laterally. Separate the edge of the spinodeltoid from the triceps and note that these heads extend proximally, deep to the spinodeltoid. The medial head of the triceps is discussed below. All three heads insert on the olecranon process of the humerus and extend the antebrachium.

Note again the position of the cephalic vein. Distally, it crosses the clavobrachialis, whereas proximally it lies on the acromiodeltoid, and then curves anteriorly, deep to the clavotrapezius. Lift the posterior margin of the

FIGURE 7.27 Muscles of the cat in lateral view.

clavotrapezius, just anterior to the acromiodeltoid, and cut through the connective tissue, fat, and nerves that you encounter. Continue to separate this muscle and the clavobrachialis from the underlying musculature. As you do so, you will see the posteriorly oriented fibers of the pectoral muscles (see below) inserting on the humerus.

Working dorsally, continue to separate the clavotrape- zius, where the levator scapulae ventralis passes deep to its margin. It is fairly easy to free the muscle here, but work carefully anterior to the acromiodeltoid. The clav­icle is present in this region, and you should avoid injur­ing the cleidomastoid (Figure 7.28), which attaches on the clavicle. Palpate for the clavicle. Once you identify its position, stop dissecting the clavotrapezius.

Superficial Forelimb Muscles: Ventral View

(Figure 7.28)

The pectoralis muscles, which draw the humerus toward the midventral line, lie superficially on the ventral surface of the thorax. Examine them in ventral view with the brachium held laterally. As a whole, this mus­culature is a triangular mass extending, on each side, from the ventral midline to the humerus. Carefully pick away at and clear connective tissue covering the muscles on one side to reveal four muscles. Once cleared, they can readily be distinguished by fiber direction. For the most part, the individual muscles are arranged in layers, one atop the other, and tend to adhere strongly to each other. Thus, do not attempt to separate the muscles by cutting them at their margins. Instead, work with a probe and needle to separate the muscles parallel to their surfaces. You do not need to separate each muscle completely; only go far enough to get an idea of the depth and extent of each.

The most superficial muscle is the pectoantebrachialis, a thin, narrow, anterior muscle that extends laterally. The epitrochlearis (which is not one of the pectorals) is a thin muscle covering the surface of the brachium posterior to the pectoantebrachialis. The epitrochlearis attaches to the olecranon of the ulna and thus extends the ante­brachium. The pectoralis major, which may be subdi­vided in two portions, lies dorsal to the latter. The more anterior part extends laterally and is covered almost entirely by the pectoantebrachialis (except for its anteri- ormost part, which is exposed in ventral view). The pos­terior part of the pectoralis major runs obliquely, with its fibers passing anterolaterally from the midline.

The pectoralis minor is the muscle lying dorsal and pos­terior to the pectoralis major. The pectoralis minor of the cat is larger than the pectoralis major, but the names are derived from human terminology, in which the pec­toralis major is indeed larger. The fibers of the pectoralis minor run even more obliquely than those of the major as they converge toward the proximal half of the humerus. The fourth muscle is the xiphihumeralis, a long, thin, and narrow muscle that lies posterior and dorsal to the pectoralis minor. For the most part, the xiphihumeralis lies along the the pectoralis minor pos­teriorly and attaches to the xiphisternum and xiphoid cartilage, which give it part of its name.

You have already noted how the fibers of the latissimus dorsi converge toward the axilla. Also note that the latissimus dorsi and the pectoralis minor adhere to one another. Carefully separate these muscles by picking away at the connective tissue that binds them, using a needle and forceps. If necessary, use a scalpel to cut them apart.

Identify the medial edge of the clavotrapezius along the neck and follow it posteriorly until it abuts against the anterior margin of the pectoral (Figure 7.28). From about this point, the muscle becomes the clavobrachialis, and its margin is bound tightly to the pectoralis major. Beginning medially, separate these muscles. You will soon be able to lift the clavobrachialis and discern the deeper part of the pectoralis, which passes diagonally beneath the clavobrachialis. You should now be able to separate the latter from the pectoralis much more easily.

Return to the medial margin of the clavotrapezius. Lift and separate it from the underlying musculature. You will uncover the cleidomastoid, mentioned above, which passes from the clavicle toward the skull. Probe deep to the sternomastoid to discern its course. Separate as much of the cleidomastoid from the clavotrapezius as possible, but work delicately near the clavicle: These muscles attach to the clavicle in close proximity, and dis­section often causes damage. Continue to pick away the fat and tough connective tissue along the medial margin of the clavotrapezius, being careful not to injure the external jugular vein. Also work deep and medial to the cleidomastoid. You should be able to separate and lift the clavotrapezius, clavobrachialis, and cleidomastoid as a unit from the underlying muscles. Clean the con­nective tissue and fat from the bend of the elbow, being careful not to injure the cephalic vein or the slender bra­chioradialis (Figure 7.27), which supinates the manus, that lies along its anterior edge.

Deep Forelimb Muscles: Lateral View (Figure 7.29) Return to the levator scapulae ventralis. Remove the fat between it and the clavotrapezius, clean away the con­nective tissue that covers it (i.e., the part deep to the clavotrapezius), and follow it anteriorly as it passes from the scapula toward the skull. Clean away connec­tive tissue deep to the levator and separate it from the underlying muscles. Once you have isolated the levator, you should easily be able to remove fat and connective

FIGURE 7.28 Muscles of the cat in ventral view.

FIGURE 7.29 Deeper muscles of the cat in lateral view.

tissue from the anterior margin of the acromiotrapezius and free the muscle from the underlying musculature. Continue posteriorly and separate the spinotrapezius from the underlying muscles. Then cut through the middle of the trapezius muscles, at right angles to the fibers, and reflect their ends.

Examine the anterior part of the latissimus dorsi beneath the spinotrapezius, and then cut the latissimus about 3 cm posterior to the brachium and reflect it. Clean off the connective tissue from the underlying musculature. Examine the muscles on the lateral surface of the scapula. The supraspinatus fills the supraspinous fossa, while the infraspinatus occupies the infraspinous fossa. These muscles insert on the greater tuberosity of the humerus. The supraspinatus extends the humerus, while the infraspinatus rotates it laterally. The teres major arises from the scapula, posteroventral to the infraspinatus. It inserts medially on the humerus, flexing and medially rotating it. Follow the long head of the triceps as it passes deep to the spinodeltoid and infraspinatus and find the teres minor, which flexes and laterally rotates the humerus. It lies along the anteroven- tral margin of the infraspinatus, from which it is initially difficult to distinguish. In Figure 7.29 the spino- deltoid is shown as cut and reflected to expose the teres minor, but it is not necessary to cut the spinodeltoid.

Pull the dorsal border of the scapula laterally and examine the muscles in dorsal view. The fibers of the rhomboideus extend anteromedially between the dorsal border of the scapula and the middorsal line. This muscle pulls the scapula toward the vertebral column. The rhomboideus capitis, extending separately as a narrow band toward the back of the skull, rotates and pulls the scapula anteriorly. The rhomboideus capitis lies on the surface of the splenius (see below), a large, flat muscle covering the neck dorsolaterally. Look ventral to the rhomboideus and note the serratus ven­tralis. It is the large muscle composed from various slips that extend between the scapula and thorax. The slips arise from the ribs and converge to insert on the verte­bral border of the scapula. The serratus ventralis will be considered again below.

Deep Forelimb Muscles: Lateral View with Forelimb Abducted (Figure 7.30)

Earlier, the latissimus dorsi was separated from the pec­toralis minor. Now separate the latissimus dorsi from the lateral thoracic wall. You will find considerable fat and connective tissue adhering to the muscle. Remove the fat and connective tissue, but do not injure the blood vessels and nerves in the axilla. At first the shoulder region will not be apparent, but it can be palpated. As you pick away tissue, the scapula and its associated musculature will come into view. When you have cleaned the musculature associated with the scapula, pull the scapula laterally to see a series of strap-like muscular slips fanning out to the thorax from the scapula. These slips are part of the serratus ventralis.

Using scissors and beginning posteriorly, make an anteroposterior cut through the pectoralis muscles about 1 cm to one side of the midline. Work your way first through the xiphihumeralis and pectoralis minor. As you do so, lift the musculature and clean away con­nective tissue beneath it to ascertain that you are cutting through pectoralis musculature only. As you approach the pectoantebrachialis, lift the musculature and look for vessels and nerves passing out of the thorax and toward the shoulder. They may be embedded in some fat. Do not injure the vessels or nerves. The most appar­ent vessel is the axillary vein, a large vein injected with blue latex. It is accompanied by the axillary artery. These vessels quickly branch into various smaller vessels. The various large nerves are part of the brachial plexus.

Continue cutting through the pectoralis major and then reflect the flaps, removing the connective tissue that binds the xiphihumeralis and pectoralis minor to the thorax, so that you can reflect the pectoral musculature completely away from the thoracic wall. Then delicately clean away connective tissue and fat from around the vessels and nerves. The nerves appear as shiny, whitish strands (some rather large) passing toward the shoulder and brachium. Most lie dorsal to the vessels, but some are anterior to them.

If the musculature has been properly cleaned, it should be easy to follow the external jugular vein posteriorly. At the level of the anterior part of the shoulder, it receives a large tributary, the transverse scapular vein (possibly already cut). The external jugular continues posteriorly to join the subclavian as it emerges from the thorax and changes its name to the axillary. When you have identified these vessels, which continue onto the forelimb, cut through the vessels as well as nerves, leaving stumps about 1 cm long emerging from the thorax.

Position the brachium as shown in Figure 7.30, and con­tinue cleaning the medial surface of the shoulder as well as the thoracic wall. Also, pick away connective tissue surrounding the vessels as they enter the shoulder musculature. Reidentify the latissimus dorsi, pectoralis muscles, and the serratus ventralis. Note how the fan­like arrangement of the serratus ventralis converges toward the dorsal border of the scapula. Note too that the posterior part of this muscle is clearly subdivided into separate slips, but its anterior fibers are arranged nearly as a continuous sheet.

FIGURE 7.30 Deeper muscles of the cat in lateral view, with forelimb abducted.

The large muscle covering the medial surface of the scapula is the subscapularis. The fibers of its various bundles converge toward the apex of the scapula and insert on the lesser tuberosity of the humerus. It is an adductor of the humerus. The teres major initially appears as one of these bundles passing along the poste­rior border of the scapula. Anteriorly, however, the sepa­ration is much clearer: Note how some of the vessels pass between the subscapularis and teres major. Carefully observe the muscles that cover the ventromedial region of the scapula. Most of the fibers belong to the subscapularis and converge toward the apex, but the small, strap-like coracobrachialis, about 0.5 cm in width, crosses against the direction of the fibers. It also adducts the humerus. In this view, the coracobrachialis lies just posterior to the origin of the biceps brachii (see below).

Examine the medial surface of the brachium. Cut through the epitrochlearis and the pectoral musculature (mainly pectoantebrachialis) covering the brachium, and reflect the ends to expose the muscles on the brachium. Clear the connective tissue. A large vessel, the brachial vein, which is a continuation of the axillary vein, should be prominently exposed. Dissect carefully near it to reveal the brachial artery (continuing from the axillary artery) and several nerves from the brachial plexus. The large muscle anterior to the vessels and nerves is the biceps brachii, and the muscle that lies posteriorly is the long head of the triceps, which has already been observed in lateral view. Dissect dor- sally to the vessels and nerves, and push them aside to expose the medial head of the triceps. Follow the biceps brachii proximally toward its origin on the scapula and reidentify the coracobrachialis. The biceps inserts distally on the radius and is a flexor of the antebrachium.

Key Terms: Muscles of the Forelimb

(See Table 7.2 for synonyms)

acromiodeltoid acromiotrapezius axillary vein biceps brachii brachial artery brachial vein brachioradialis cephalic vein clavobrachialis clavotrapezius cleidomastoid coracobrachialis epitrochlearis

external jugular vein external oblique infraspinatus latissimus dorsi levator scapulae

ventralis lumbodorsal fascia mandibular gland parotid gland pectoantebrachialis pectoralis major pectoralis minor rhomboideus

rhomboideus capitis serratus ventralis spinodeltoid spinotrapezius splenius sternomastoid subscapularis supraspinatus

teres major

teres minor

transverse scapular vein triceps brachii: lateral head; long head; medial head

xiphihumeralis

Muscles of the Hind Limb

Table 7.3 lists the hind limb musculature and indicates their origin, insertion, and main functions.

Superficial Hind Limb Muscles: Lateral View (Figure 7.31)

The skin of the hind limb has already been removed. Carefully pick away the connective tissue and fat on the lateral surface of the hind limb and the base of the tail, but take care not to injure the fascia that covers the musculature. Considerable fat is present in the popliteal fossa, the depression posterior to the knee joint. Carefully clear this region. You may notice the oval popliteal lymph node, which is embedded within the fat.

Examine the musculature. The most conspicuous muscle of the thigh is the biceps femoris. This large muscle covers much of the posterior half of the thigh and is a main adductor and extensor of the thigh. It has a narrow origin dorsally from the ischial tuberosity but widens distally to insert by an aponeurosis on the patella and the proximal portion of the tibia. The pos­terior portions of two deeper muscles, the semitendi­nosus and semimembranosus, are exposed posterior to the dorsal part of the biceps femoris.

Next, identify the sartorius, which lies along the ante­rior edge of the thigh. In lateral view this muscle appears to be elongated and narrow, but its more extensive medial portion will be seen shortly. Posterior to the dorsal portion of the sartorius is the gluteus medius, which is covered by fascia. Carefully remove the fascia to uncover the muscle, as shown in Figure 7.31. Poste­rior to it is the smaller gluteus superficialis, followed by the gluteofemoralis. The latter is a strap-like muscle that continues distally, deep to the biceps femoris. The gluteal musculature generally functions in abducting the thigh. Extending between the origin of the biceps femoris and the posterior margin of the gluteofemoralis, identify the obturatorius internus. Dorsal to it, extend­ing from beneath the posterodorsal margin of the glu- teofemoralis to the ventral surface of the tail, is the coccygeus.

FIGURE 7.31 Superficial muscles of the hind limb of the cat in lateral view.

The tensor fasciae latae, a flexor of the thigh, is ventral to the gluteal musculature noted above. From its narrow dorsal origin, it fans out distally and inserts on the fascia lata, the tough membrane that extends toward the knee joint, anterior to the biceps femoris. The tensor fasciae latae is subdivided into a longer anterior portion and a triangular posterior portion. Trace the anterior portion as it extends deep to the sartorius and onto the anterior surface of the thigh.

The tenuissimus is a ribbon-like muscle that lies almost entirely deep to the biceps femoris. It will be exposed presently. Its very distal end, however, is exposed in lateral view along the posterodistal edge of the biceps femoris. Look for this exposed portion. It inserts by a short tendon that merges with that of the biceps femoris. When you have identified it, lift the posterior edge of the biceps femoris and gently scrape the loose connec­tive tissue adhering to its deep surface to locate the rest of the tenuissimus. It extends dorsally and passes deep to the very dorsal portion of the gluteofemoralis (see Figure 7.33). It may serve as an extensor of the thigh or flexor of the crus, but its composition (a high number of muscle spindles) as well as size suggest that it may function as a tension sensor.

Superficial Hind Limb Muscles: Medial View

(Figure 7.32)

Clear away connective tissue from the medial surface of the thigh, but leave the crural fascia for the time being.

FIGURE 7.32 Superficial muscles of the hind limb of the cat in medial view.

Avoid damaging vessels and nerves. Note again the wad of fat that lies between the body wall and the proximal surface of the thigh. In males the spermatic cords extend through this wad as they pass from the body wall to the testes. Dissect carefully to avoid injuring the spermatic cords. They are shown as having been dissected out in Figure 7.32, but you do not need to expose them to the same extent.

Once the surface of the thigh has been cleared of connec­tive tissue, the full extent of the sartorius, already observed in lateral view, may be appreciated. It covers the anteromedial surface of the thigh. The large muscle on the posteromedial surface is the gracilis muscle, which flexes the crus and adducts the thigh. The distal portion of the semitendinosus is exposed just posterior to the gracilis. Distally the sartorius and gracilis con­verge and lie side by side, with the former partially cov­ering the latter, as they extend toward the knee. Examine the triangular region formed between their proximal portions and the body wall. The femoral artery and femoral vein are the conspicuous vessels emerging from within the body cavity and extending distally. The small muscle just anterior (keep in mind that the limb is essen­tially parasagittal in position) to the very proximal end of these vessels is the iliopsoas, which flexes and rotates the thigh. The femoral nerve lies anterior to the femoral vessels and passes over the iliopsoas. Probe between the iliopsoas and sartorius to identify the vastus medialis, which will be exposed shortly. Posterior to the vessels is the pectineus, a small, triangular adductor of the thigh, followed by the larger adductor longus, and the much larger adductor femoris, much of which lies deep to the gracilis. The last two muscles are also adductors of the thigh (but see also Table 7.3).

Examine the vessels more closely. They will be discussed in more detail later, but it is worth noting the main branching patterns at this time. The femoral artery and vein are the main continuations of the external iliac artery and external iliac vein, which lie within the body cavity (see pages 204 and 205). The femoral artery and vein are therefore the most conspicuous vessels on the medial surface of the thigh. However, the external iliac vessels branch just as they approach the body wall. The external iliac artery gives rise to the femoral artery and the deep femoral artery, and the external iliac vein is formed by the confluence of the femoral vein and the deep femoral vein. It is these four vessels that perforate the body wall onto the thigh. As noted, the femoral vessels are easily observed, but the deep femoral vessels may also be identified. Pick away the body musculature adjacent to the femoral artery, working your way toward the abdominal midline. The much smaller deep femoral artery, extending posteromedially, will be exposed. In many individuals, one of its branches is the external pudendal artery, which extends medially into the wad of fat in the groin region to supply the exter­nal genitalia. The external pudendal vein follows the artery. In males the artery and vein pass dorsal to the spermatic cord. Follow the deep femoral artery, after the origin of the external pudendal artery, as it passes into the musculature. The deep femoral vein follows the artery but lies more deeply. Move the artery to expose the vein.

Return to the femoral artery and femoral vein. The lateral circumflex artery and the lateral circumflex vein branch from these vessels a short distance distally. Note the saphenous nerve that accompanies the vessels. More distally, nearer the knee, the saphenous artery and saphenous vein branch from the femoral vessels and extend distally on the surface of the crural fascia. The saphenous nerve accompanies them.

Deep Hind Limb Muscles: Lateral View

(Figures 7.33-7.35)

Examine the lateral surface of the thigh. Continue to scrape away the connective tissue and fat from between the deep surface of the biceps femoris (working from both its anterior and posterior margins) and the under­lying musculature, and lift the biceps from the muscu­lature. Make an anteroposterior cut through the central part of the biceps femoris and reflect its ends. The exposed surface must be cleared of connective tissue and fat to produce a dissection similar to that presented in Figure 7.33. Although this is tedious, it furnishes an excellent example of how connective tissue and fat are distributed between muscles, both to provide a plane along which muscles may move against each other and to provide protection for structures such as nerves. In clearing the region, preserve the conspicuous ischiadic nerve (Figure 7.34) but remove or cut through blood vessels.

The ischiadic nerve extends nearly parallel to the tenuis­simus muscle. Note the distal end of the gluteofemoralis. Its fibers insert into a narrow, tapered tendon, which is nearly as long as the fleshy part of the muscle and extends toward the knee joint. The tendon may be dis­tinguished most easily distally, where it lies on the pos­terior surface of the fascia lata, and appears as a narrow, glistening ribbon. Separate it from the fascia lata.

Reflection of the biceps femoris also exposes two muscles already identified above, the semitendinosus and, anterior to it, the semimembranosus. The adduc­tor femoris lies anterior to the latter, deep to the ischiadic nerve. Just anterior to the origin of the biceps femoris and ventral to the obturatorius internus, iden­tify the gemellus caudalis and the quadratus femoris.

Poke a small opening into the fascia lata, ventral to the level of the tensor fasciae latae. Insert a scissor blade into the opening, bisect the fascia anteroposteriorly, and lift it from the underlying muscle. Cut along the poste­rior edges of the fascia where it meets the adductor femoris (avoid cutting the tendon of the glute- ofemoralis), and then reflect its flaps. The tensor fasciae latae will be reflected with the proximal flap of the fascia lata. The large muscle exposed is the vastus lateralis. Clear away connective tissue along the anterodorsal margin of this muscle to expose a portion of the rectus femoris. The tendon of the gluteus profundus (see below) should also be visible. The vastus intermedius has a small, narrow exposure along the posterodistal margin of the vastus lateralis. The vastus lateralis, vastus intermedius, vastus medialis (identified above, but see also below), and rectus femoris form the muscle complex termed the quadriceps femoris, which is the main musculature that extends the crus. The capsularis

FIGURE 7.33 Deep muscles of the hind limb of the cat in lateral view.

is a small, narrow muscle just anterior to the hip joint. It extends from the ilium to the anteroproximal surface of the femur. To locate it, probe between the origin of the vastus lateralis and the posteroventral margin of the gluteus profundus (Figure 7.34). Its small size and high proportion of muscle spindles suggest it functions as a tension sensor, although its position indicates a thigh flexor function.

Cut anteroposteriorly through the belly of the gluteo- femoralis and reflect it, along with the tenuissimus. Free the gluteus maximus and gluteus medius muscles from underlying musculature. Cut anteroposteriorly through the center of each muscle and reflect them, as shown in Figure 7.34, to expose the underlying muscles. The gluteus minimus (noted above), with its con­spicuous insertion tendon, is the more anterior. The

FIGURE 7.34 Deep muscles of the hind limb of the cat in lateral view.

piriformis lies more posteriorly, and largely covers the gemellus cranialis, two muscles that act mainly to abduct the thigh.

Reflect the gluteofemoralis anteriorly, as shown in Figure 7.35. Carefully cut dorsoventrally through the middle of the quadratus femoris, but do not injure underlying musculature. Continue cutting dorsally through the gemellus caudalis and obturatorius inter­nus. Reflect the ends of the muscles you have cut through to expose the obturatorius externus, which extends anteroposteriorly.

Examine the muscles on the lateral surface of the crus by removing the crural fascia (Figure 7.33). There are actually several layers of fascia in the region, and they have been separated and partially cut away to produce the dissection in Figure 7.33, which preserves the inser­tions of the biceps femoris and tenuissimus. The most conspicuous muscle on the crus is the gastrocnemius, which lies posteriorly and has lateral and medial heads. Its proximal portion is very thick, but it tapers distally into its tendon, the gastrocnemius tendon. A smaller muscle, the soleus, lies mainly deep to the gastrocne­mius, but a small portion is exposed anterior to it. It is also thick proximally and tapered distally. The tendons of the gastrocnemius and soleus muscles pass together through a sheath formed by the fascia as the calcaneal tendon, which inserts on the proximal end of the calca­neum. As their tendons converge, the soleus and gas-

FIGURE 7.35 Deep muscles of the hind limb of the cat in lateral view.

trocnemius, which are the main extensors of the pes, are collectively termed the triceps surae muscle.

The tibialis anterior lies on the anterior surface of the crus. Posterior to it is the slender, elongated extensor digitorum longus. Follow the latter distally into its thick tendon on the dorsal surface of the pes. Between the extensor digitorum longus and the soleus is the peroneus musculature. A prominent nerve, the superficial per­oneal nerve, lies between the extensor digitorum longus and the peroneus muscles. Three peroneus muscles may be recognized. The peroneus longus is an elongated muscle lying posterior to the extensor digitorum longus. Follow it distally as it tapers into its prominent tendon, which passes along a groove on the lateral surface of the lateral malleolus of the fibula (see page 149). The peroneus tertius is a smaller muscle posterior to the peroneus longus. It may be difficult to isolate, but its narrow tendon lies posterior to the tendon of the per­oneus longus. The peroneus brevis is larger and exposed posterior to the peroneus tertius. Its tendon is much larger and easily identified. The tendons of the peroneus tertius and peroneus brevis extend distally adjacent to each other, and both pass along a groove on the poste­rior surface of the lateral malleolus. As they pass dis­tally, the tendon of the peroneus brevis obscures that of the peroneus tertius.

Deep Hind Limb Muscles: Medial View

(Figure 7.36)

Return to the medial surface of the hind limb. Lift the sartorius by separating it from underlying musculature. Cut across its central portion and reflect its ends. Do likewise for the gracilis. This will expose much of the

FIGURE 7.36 Deep muscles of the hind limb of the cat in medial view.

musculature that has already been identified. Anteriorly, identify the vastus medialis. Much of its anterior margin is bordered by the rectus femoris. Recall that the tensor fasciae latae and fascia lata, which was cut earlier (as shown in Figures 7.35 and 7.36), lies on the vastus lat­eralis. More posteriorly, note the adductor femoris and semimembranosus, both now uncovered. The semi­tendinosus inserts on the tibia just distal to the insertion of the semimembranosus. The lateral-to-medial orienta­tion of these last two muscles and their contribution to the medial wall of the popliteal fossa is easily appreciated.

Remove the crural fascia from the medial surface of the crus. Clear away connective tissue. The medial head of the gastrocnemius is the conspicuous muscle posteriorly. Probe deep to its anterior margin, where the gastro­cnemius begins to taper distally, to locate the soleus, already observed in lateral view, and the plantaris, lying between the soleus and gastrocnemius. The tendon of the plantaris extends through the crural sheath with the calcaneal tendon. It continues around the proximal end of the calcaneum onto the plantar surface of the pes, and extends distally onto the digits. Here, the small flexor digitorum brevis muscle surrounds the tendon and contributes to flexion of the digits.

The large tibialis nerve emerges from beneath the mus­culature. Carefully dissect around the nerve to free it from surrounding structures, and follow it as it extends toward and then around the posterior margin of the medial malleolus of the tibia (see page 149). The medial surface of the tibia is the white strip of bone extending proximodistally near the anterior margin of the crus. On its anterior surface is the tibialis anterior, identified earlier. Follow it distally into its tendon and note that it extends medially across the proximal surface of the pes. Examine the musculature posterior to the tibia. Near the insertion of the semitendinosus, locate the popliteus, consisting of a faint, thin band of fibers extending posterodorsally from the tibia. The popliteus, which flexes the crus and rotates the tibia medially, curves laterally and crosses the posterior side of the knee joint to its origin on the lateral epicondyle of the femur. The flexor digitorum longus is the larger mass of mus­culature just posterior to the tibia. Follow it distally. Its tendon is nearly parallel and anterior to the tibialis nerve, and is of similar thickness. The tendon curves around the posterior margin of the medial malleolus onto the medial surface of the pes. Anterior to the tendon of the flexor digitorum longus is the thicker tendon of the tibialis posterior muscle. It also curves around the malleolus onto the medial surface of the pes. The fibers of the tibialis posterior lie almost entirely deep to the flexor digitorum longus. You may cut through the latter to expose the tibialis posterior.

Key Terms: Muscles of the Hind Limb

adductor femoris adductor longus

(adductor femoris longus)

biceps femoris calcaneal tendon

(Achilles tendon) capsularis (articularis

coxae) coccygeus (abductor

caudae internus)

deep femoral artery deep femoral vein extensor digitorum

longus

external iliac artery external iliac vein external pudendal artery external pudendal vein fascia lata femoral artery femoral nerve femoral vein flexor digitorum longus gastrocnemius gemellus caudalis

(gemellus inferior) gemellus cranialis

(gemellus superior) gluteofemoralis

(caudofemoralis, coccygeofemoralis, gluteobiceps)

gluteus medius gluteus profundus

(gluteus minimus) gluteus superficialis

(gluteus maximus) gracilis iliopsoas ischiadic nerve lateral circumflex artery lateral circumflex vein

obturatorius externus obturatorius internus pectineus peroneus brevis

(fibularis brevis)

peroneus longus

(fibularis longus)

peroneus tertius

(extensor digitorum lateralis)

piriformis (pyriformis) plantaris (flexor

digitorum superficialis)

popliteus quadratus femoris quadriceps femoris

(= rectus femoris + vastus intermedius + vastus lateralis + vastus medialis) rectus femoris saphenous artery saphenous nerve saphenous vein sartorius semimembranosus semitendinosus soleus tensor fasciae latae tenuissimus (abductor

cruris caudalis)

tibialis anterior (tibialis

cranialis)

tibialis posterior (tibialis caudalis)

triceps surae

(= gastrocnemius + soleus)

vastus intermedius vastus lateralis vastus medialis

Muscles of the Head and Trunk

Table 7.4 lists the head and trunk musculature and indi­cates their origin, insertion, and main functions.

Muscles of the Trunk (Figures 7.28-7.30)

The musculature forming the abdominal wall is arranged mainly as three thin, but extensive, muscular sheets or layers (Figure 7.28). The most superficial layer is the external oblique (which you noted previously), the middle layer is the internal oblique, and the medial layer is the transversus abdominis. A fourth muscle, the rectus abdominis, also contributes to the abdominal wall. It forms a ventral muscular band running anteroposteri- orly between the sternum and pelvis (Figure 7.30). These four muscles act to constrict the abdomen. The rectus can also draw the ribs and sternum posteriorly, flexing the trunk.

The fibers of the external oblique extend posteroven- trally. They do not extend all the way to the midventral line but attach by way of an aponeurosis, which covers the deeper musculature of the ventral surface of the abdomen. To see the deeper muscles, cut a smal flap in the external oblique, in the central part of the abdomen, as in Figure 7.28. Reflect the muscle and aponeurosis. You can now see the middle layer, the internal oblique. Its fibers extend anteroventrally, nearly at right angles to those of the external oblique. Note, though, that the internal oblique also does not extend to the midventral line, but is continued by an aponeurosis. The muscle lying deep to the aponeuroses is the rectus abdominis, and it will be seen clearly when the internal oblique is cut and reflected. To do so, cut a similar flap in the inter­nal oblique and reflect the muscle and aponeurosis. The muscle exposed is the transversus abdominis, the deepest layer. In this region of the abdomen, the ventral end of the muscle dips deep to the rectus abdominis. Lift the lateral margin of the rectus abdominis. The trans­versus abdominis is also continued to the midventral line by an aponeurosis. The relative positions of the transversus abdominis and rectus abdominis muscle change more posteriorly. There, the aponeurosis of the former divides so that part of it also covers the rectus abdominis.

Next, examine muscles associated with the thorax. The scalenus (Figure 7.30) lies laterally on the thorax, along the ventral parts of the serratus ventralis. Posteriorly, it is subdivided into three narrow bands, with the middle part usually extending farthest posteriorly. Anteriorly, they unite into a single band that passes along the neck. The transversus costarum is a small, thin sheet. Its fibers extend anterodorsally from the sternum toward the ventral band of the scalenus, where it inserts on the first rib. The longus colli is a long, narrow muscle situated ventral to the cervical vertebrae. It extends anteropos- teriorly between the anterior part of the scalenus and the external jugular vein. Note also the longitudinal muscle ventral to the posterior part of the external jugular. It is the posterior end of the sternohyoid muscle, which will be considered again below.

The thoracic wall is formed mainly by musculature that extends between successive ribs. As in the abdominal region, there are three main muscles. Most superficially are the external intercostals (Figure 7.29), followed by the internal intercostals, and, most medially, the trans­versus thoracis. Of these, only the internal intercostals extend from middorsally to midventrally. To see the first two muscles, examine the thoracic wall posterior to the serratus ventralis. The muscle fibers extending slightly posteroventrally between successive ribs are external intercostals. Carefully cut perpendicularly through the fibers of one set of external intercostals to expose the internal intercostals, whose fibers run steeply pos­terodorsally. The external intercostals do not extend all the way to the midventral line, but end at about the level of the lateral margin of the rectus abdominis. Locate the latter muscle and lift its lateral portion away from the thoracic wall. Near the midventral line, note that the internal intercostals are exposed between the ribs. The transversus thoracis is present only near the mid- ventral line, deep to the internal intercostals. Its fibers run almost transversely, with a slight posteroventral inclination. It is best viewed when the thoracic cavity is opened (see Figures 7.45 and 7.51).

Muscles of the Back and Neck (Figure 7.37)

Two thin muscular sheets, the serratus dorsalis cranialis and serratus dorsalis caudalis, lie over the back, deep to the latissimus dorsi and rhomboideus (Figure 7.30). The serratus dorsalis muscles are composed of slips extend­ing from the middorsal line to the lateral surfaces of the ribs. The fibers do not extend all the way middorsally, but attach by aponeuroses. The fibers of the serratus dorsalis cranialis extend posteroventrally, and those of the serratus dorsalis caudalis extend anteroventrally.

Next examine the dorsal back or epaxial muscles (Figure 7.37), which lie deep to the musculature so far observed and act mainly to extend the vertebral column. This musculature is extensive, lying between the neural spines and transverse processes and proximal ends of the ribs, from the ilium to the cervical region. It is complex largely because its individual muscles extend between various parts of more posterior vertebrae to more anterior vertebrae, and fusion among its different parts occurs, particularly posteriorly.

Begin your examination posteriorly with the muscles of the lumbar and posterior thoracic regions. Make a lon­gitudinal cut through the fleshy part of the serratus dor­salis muscles and reflect them. To examine the back

TABLE 7.4 Muscles of the head and trunk

TABLE 7.4 Continued

FH]

LLV

FIGURE 7.37 Dorsal muscles of the neck and back of the cat in dorsolateral view.

musculature here, you must also cut through the lum- bodorsal fascia, as follows. Poke a hole through the fascia about midway along its length, 0.5 cm to one side of the neural spines. There are two main fascial layers. Separate them by passing a blunt probe between them. Cut through the superficial layer longitudinally, going forward as far as its anterior limit and back to about the level of the anterior part of the hind limb. Continue to remove the connective tissue and fat deep to this fascial layer—note that the latissimus dorsi arises from it laterally.

Clean the surface of the deep layer of fascia to deter­mine its limits. Lateral to the sheet is a longitudinal and relatively narrow muscle bundle, the most lateral portion of the longissimus dorsi musculature. You should also be able to faintly see muscle bundles through the fascia. Cut through this deeper fascia, using the same method as with the superficial layer. In this case, dissection is essentially confined to the lumbar region, because you will not be able to go as far anteri­orly, as muscle fibers adhere strongly to the deep surface of the fascia. Reflect the fascia to uncover three more longitudinally arranged muscle bundles. The most medial, as well as the narrowest, is the multifidus. It is an extensive muscle that is best seen in the lumbar region, lying next to the neural processes. It passes ante­riorly deep to other muscles of the back into the cervi­cal region. The two lateral bundles are part of the longissimus dorsi, which is therefore subdivided into three bundles in this region. Its two lateral bundles, sep­arated by the thoracolumbar fascia, are considered to form the lateral division of the longissimus dorsi. The medial bundle is considered the medial division of this muscle.

Further anteriorly, in the thoracic region, the longis­simus musculature continues forward as three sub­divisions, but these do not correspond entirely to those observed in the lumbar region. To see the more anterior muscles, reflect the anterior part of the latissimus dorsi (along its middorsal origin), as well as the serratus dorsalis. The three subdivisions of the musculature, arranged as longitudinal bundles and derived from the more posterior portion of the longissimus, may now be identified. The spinalis dorsi is the most medial, fol­lowed by the anterior continuation of the longissimus dorsi, and then, most laterally, by the iliocostalis. The spinalis dorsi arises mainly from the deep layer of the thoracolumbar fascia. Follow the longissimus dorsi anteriorly into its cervical extension, the narrow longis­simus capitis, which lies along the ventral margin of the splenius on the neck. The latter was identified earlier as being deep to the rhomboideus capitis. The splenius and longissimus capitis tend to fuse, but they should be clearly demarcated. Separate these muscles, cut through the middle of the splenius, and reflect its ends. The two muscles thus exposed are the semispinalis capitis and semispinalis cervicis (which is actually the anterior portion of the multifidus, noted above), which pass forward from the vertebrae to insert on the skull. The longus colli, passing ventrally along the neck between the anterior part of the scalenus and the external jugular vein, was identified earlier.

Muscles of the Throat and Jaw

(Figures 7.28, 7.38, and 7.57)

Examine the muscles associated with the jaws, throat, and tongue, many of which are small, thin, strap-like muscles. It is useful to be familiar with the meaning of the main roots used in names of these muscles (hyo- refers to the hyoid, thyro- to the thyroid cartilage, genio- to the chin, glossus to the tongue). Reidentify the sternomastoid, and examine it in ventral view. The sternomastoid from each side passes ventrally and posteriorly from the occiput of the skull. Each follows the anterior border of the clavotrapezius dorsally, but as it nears the throat the sternomastoids veer medially and meet in a V at the base of the throat. The muscles of the throat lie mainly between the V. Gently spread apart the sternomastoids to expose this musculature. Pick away the connective tissue from the surface of the musculature, being careful not to injure the veins passing through the region. Examine the external jugular veins, and note that each receives a medial branch that together form the transverse jugular vein near the anterior end of the throat. Extending from this union is a small vessel that passes between the musculature.

The most superficial muscles covering the throat are the sternohyoid muscles, whose posterior portions were seen earlier along the neck ventral to the external jugular vein. On the throat, these thin, narrow muscles pass anteroposteriorly next to each other at the midline. Separate them at the midline. Lift one of them from the underlying muscles, cut it, and reflect the ends. You will uncover another set of longitudinal fibers, dorsal and slightly lateral to the sternohyoid. These are parallel to those of the sternohyoid and appear at first glance to constitute a single muscle, but they are two muscles, lying end to end. The posterior and longer muscle is the sternothyroid; the more anterior and shorter is the thy­rohyoid (Figure 7.38). Gently pass a blunt probe beneath them to determine their extent.

Examine the muscles anterior to the transverse jugular vein. This area is roughly triangular, with the sides of the triangle formed by the digastric muscles. They lie along the medial edges of the dentary and converge toward the mandibular symphysis. Between the digastrics is the mylohyoid, which actually consists of a pair of muscles connected by a raphe at the midline. It is easily recognizable by its transverse and slightly

FIGURE 7.38 Muscles of the throat of the cat in ventral view.

curving fibers. Extending laterally along the posterior edge of the mylohyoid from the lateral edge of the ster­nohyoid is the very small and narrow stylohyoid. The deeper muscles of the throat and tongue lie beneath the mylohyoid. To view them, cut and reflect the mylohy­oid along the midline. The thin, narrow geniohyoid muscles (see also Figure 7.40) extend anteroposteriorly next to each other at the midline. These arise from the dentary on either side of the manibular symphysis (the region of the chin in humans; cats do not have a true chin) and insert on the hyoid. The narrow hyoglossus muscle arises deep and lateral to the insertion of the geniohyoid. Its fibers pass anteriorly into the tongue and its surface is crossed by the hypoglossal nerve and lingual artery. The genioglossus muscle arises anteriorly, lateral and deep to the origin of the geniohyoid, and passes posterodorsally into the tongue. The styloglossus is a long, narrow muscle that passes from the mastoid process of the skull into the tongue. It extends forward parallel to the medial border of the dentary. Push the digastric laterally to help locate the styloglossus. It will cross the anterior part of the hyoglossus. The mass of the tongue is formed mainly by intrinsic fibers, termed the lingualis proprius, within the tongue (Figure 7.40). Examine the head. The larger muscle covering the posterolateral surface of the jaw is the masseter, one of the three main jaw-closing muscle groups (Figures 7.27, 7.29, 7.30, and 7.39). The temporalis, another jaw­closing muscle, lies on the lateral surface of the cranium and arises from the temporal fossa (see page 133). It is deep to the parotid and mandibular glands, large sali­vary glands that will be described presently, and covered by a thick fascia. A small slip of the temporalis, the pars zygomatica, curves over the zygomatic arch (Figure

7.37). The third and smallest jaw-closing muscle, the pterygoid, lies medial to the jaw and requires further dissection. It is not considered further.

Key Terms: Muscles of the Head and Trunk

digastric external intercostals genioglossus geniohyoid hyoglossus iliocostalis

internal intercostals internal oblique lingualis proprius longissimus capitis longissimus dorsi longus colli masseter multifidus mylohyoid rectus abdominis scalenus

semispinalis capitis semispinalis cervicis serratus dorsalis caudalis

serratus dorsalis cranialis

spinalis dorsi sternohyoid sternothyroid styloglossus stylohyoid temporalis thyrohyoid transverse jugular vein transversus abdominis transversus costarum transversus thoracis