Section V-Cardiovascular System

Heart

The heart lies within the pericardial cavity, which is iso­lated from the mediastinum by the pericardium (see page 186). To complete the study of the heart and its vessels, remove the pericardium carefully, especially near the roots of the lungs and where the great vessels leave the heart (see Figure 7.45).

On the ventral surface of the heart, the separation of the ventricles is marked by the interventricular groove, which passes anteriorly on the left to posteriorly on the right and is often filled with fat. A similar interventric­ular groove is also present on the dorsal surface of the heart. The separation between the atria and ventricles is represented by the coronary sulcus, which is also usually filled with fat. The lateral extension of each atrium is the auricle (Figures 7.52 and 7.53), which has scalloped margins and is usually darker than the rest of the heart tissue. The great vessels that leave the heart anteriorly pass between the left and right auricles.

Before examining the other structures of the circulatory system, it is useful to review the basic flow of blood. Oxygen-depleted blood from the body returns to the right atrium through the anterior and posterior venae cavae (sing., vena cava). From there, it is pumped to the right ventricle, which pumps it through the pulmonary arteries to the lungs for reoxygenation. From the lungs, oxygenated blood returns to the heart via the pul­monary veins to the left atrium. The blood then enters the left ventricle, which pumps it through the aorta and arteries to the rest of the body.

Vessels

Main Vessels Associated with the Heart

The great vessels leave the base of the heart (Figures 7.45, 7.55). The pulmonary trunk leads from the right ventricle. It is located on the middle part of the ventral surface and angled toward the left. The aorta, carrying blood from the left ventricle, extends anteriorly just dorsal to the pulmonary trunk and medial to the right auricle. It curves sharply to the left as the aortic arch, and then posteriorly, passing dorsal to the root of the left lung, as the thoracic aorta (Figure 7.51). Dissect carefully between the aortic arch and pulmonary trunk to find a tough ligamentous band connecting these vessels. This is the ligamentum arteriosum, a remnant of the ductus arteriosus, through which blood was shunted in the fetus.

The pulmonary trunk is very short and divides almost immediately into left and right pulmonary arteries (injected with blue latex). The left pulmonary artery is clearly discernable as it passes laterally to the left lung. The right pulmonary artery passes under the aortic arch to reach the right lung. Blood from the lungs returns to the left atrium through left and right pulmonary veins (injected with red latex), which are easily seen ventrally on the roots of the lungs (Figure 7.51). Blood from the body returns to the heart via the venae cavae. The ante­rior vena cava, draining the region anterior to the diaphragm, has already been noted during dissection of the mediastinum. The posterior vena cava drains the regions posterior to the diaphragm. Lift the right side of the heart and note these vessels entering the right atrium (Figures 7.42, 7.43, and 7.53).

The peripheral distribution, including the main branches and tributaries, of vessels that leave the heart is treated in the following sections.

Vessels Anterior to the Diaphragm

The vessels described here are branches of the aortic arch and thoracic aorta and tributaries of the anterior vena cava, which, respectively, mainly supply and drain the regions of the body anterior to the diaphragm. The summit of the aortic arch gives rise to two main vessels (Figures 7.55 and 7.56). The larger, on the right, is the brachiocephalic artery; the other is the left subclavian artery. The anterior vena cava lies just to the right of the brachiocephalic artery. To trace these vessels anteriorly, remove the connective tissue (including the thymus, which may be rather large in younger specimens) and fat associated with them, but avoid injuring the nerves.

Begin by tracing the main tributaries of the anterior vena cava (Figures 7.53 and 7.54). One or two small branches arise from the anterior vena cava, but its most posterior branch is the azygos vein (Figures 7.44, 7.53, and 7.54) from the dorsal surface of the vena cava; lift the heart to observe it. The azygos passes a very short distance dorsally, turns abruptly posteriorly, and then passes dorsal to the root of the right lung along the right side of the body. It mainly drains the intercostal areas posterior to the heart through the intercostal veins from both sides of the body. The anterior intercostal areas are drained by the highest intercostal veins. That of the right side often enters the anterior part of the azygos, but may enter the vena cava directly, a short dis­tance anterior to the azygos. The left highest intercostal vein typically enters the left side of the vena cava between the second and third ribs. The intercostal arter­ies and highest intercostal arteries that supply these areas extend closely in parallel with the veins; their origins are considered below.

The next large branch, the internal mammary vein, enters the ventral surface of the anterior vena cava.

FIGURE 7.51 Thoracic cavity of the cat in ventral view, showing respiratory system, vessels, and nerves.

(Figure 7.45). The left and right internal mammary arteries run, for most of their length, parallel to the veins. A short distance anterior to the internal mammary vein, the anterior vena cava is formed by the confluence of the left and right brachiocephalic veins. The tributaries of the brachiocephalic veins are similar but usually not symmetric. The costocervical + vertebral trunk, a large vein formed by the confluence of the cos­tocervical vein and vertebral vein, commonly enters the right brachiocephalic dorsolaterally just before or very near the union of the right and left brachiocephalic veins. On the left side, the costocervical + vertebral trunk usually enters the left brachiocephalic slightly more anteriorly. In either case, the trunk curves dorsally. Follow the trunk to observe its tributaries. The verte­bral vein heads almost directly anteriorly, whereas the costocervical heads mainly laterally and then posteri­orly. In some specimens the right costocervical and ver­tebral veins have separate entrances, as is shown in the right side of Figure 7.54.

The brachiocephalic is typically formed by the subcla­vian vein and bijugular trunk, large vessels that unite just medial to the first rib. The subclavian passes later­ally and helps drain the forelimb. The bijugular trunk is a very short vessel formed by the large external jugular vein and the much smaller internal jugular vein. The external jugular passes anteriorly along the lateroventral surface of the neck, whereas the internal jugular vein passes more medially along the neck. The internal jugular primarily drains the palate, pharynx, and inside of the skull, and may not be injected.

The external jugular helps drain two main areas, the forelimb and the external structures of the head. Drainage of the forelimb is accomplished through its first

FIGURE 7.52 Heart and vessels of the cat in dorsal view.

main tributary, the transverse scapular vein. As was observed earlier (page 163), this vessel enters the exter­nal jugular at about the level of the front of the shoulder. A main tributary of the transverse scapular is the cephalic vein, also observed earlier passing along the lateral surface of the forelimb (page 158). Further anteri­orly the external jugular has three main tributaries, but their branching patterns vary (Figures 7.39 and 7.54). Often, they converge close together to form the external jugular. The transverse jugular vein forms a ventral link between the left and right external jugular veins, and helps drain the neck. The anterior facial vein passes ante­riorly to the face and lower jaw. The posterior facial vein extends anterodorsally, crosses the mandibular gland, and passes deep to the parotid gland (see page 180).

Return to the aortic arch, and reidentify the brachio­cephalic and left subclavian arteries (Figures 7.55 and 7.56).

The brachiocephalic artery heads anteriorly, just medial to the anterior vena cava. At about the level of the inter­nal thoracic vein, it gives rise to three branches, the right subclavian artery, and the right and left common carotid arteries. The subclavian lies most laterally, while the common carotids pass anteriorly on either side of the trachea. The arteries pass deep to the anterior vena cava and brachiocephalic veins. The left common carotid sometimes arises independently, with the right common carotid and right subclavian arising further distally from

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FIGURE 7.53 Vessels and nerves anterior to the heart of the cat in ventral view.

a very short common trunk. All three arteries, however, may arise very close together.

As the common carotids ascend the neck, they send out various small branches to supply the thyroid gland, muscles, and lymph nodes. Note the nerves present in this region. The phrenic and vagus nerves were observed passing through the thorax (Figures 7.42 and 7.43). In the cervical region, the vagus and the anterior extension of the sympathetic trunk (Figure 7.53) form the vagosympathetic trunk, which is bound together with the common carotid artery and internal jugular vein by a tough connective sheath. The vagus and sympathetic trunk separate near the branching of the brachiocephalic

FIGURE 7.54 Schematic illustration of the veins anterior to the heart of the cat in ventral view.

artery. The sympathetic trunk extends anteroposteriorly along the dorsal wall of the thorax, crossing ventral to the intercostal arteries and veins. Carefully dissect it out, and note the series of small ganglia along its course.

Follow one of the common carotids as it approaches the skull, near which it divides. Its main branch is the exter­nal carotid artery, which is as wide as the common carotid, so the division is not readily apparent (Figure 7.57). Find the branching point as follows. A short dis­tance posterior to the masseter muscle, locate the hypoglossal nerve, which was observed earlier (page 179). The nerve crosses the very proximal part of the external carotid artery, so the division of the common carotid occurs just posterior to the nerve. Carefully dissect along the dorsal surface of the common carotid, just posterior to the hypoglossal nerve. In most mammals three small arteries usually arise in very close proximity. These are the internal carotid, occipital, and ascending pharyngeal arteries; the last two usually arise by a short, common trunk. These arteries can be dissected, but they may be difficult to find because they are small, are closely bound by connective tissue, and in the cat one of the arter­ies, the internal carotid artery, is largely occluded and rep­resented by a whitish strand, the internal carotid ligament (only the proximal portion of the internal carotid artery is occluded. Its distal part, within the skull, remains func­tional, receiving blood via anastomoses with other arter­ies, such as the maxillary and ascending pharangeal.). The arteries and ligament pass anterodorsally, with the liga­ment being most posterior of the three. Thus, even though they arise almost together with the internal carotid liga­ment, the occipital and ascending pharyngeal arteries are actually the first branches of the external carotid artery. The ligament extends nearly dorsally, and so is not visible in Figure 7.57. These three small vessels may be observed, but this requires time and delicate dissection. If you cannot find them, use the hypoglossal nerve as a landmark to indicate the beginning of the external carotid.

The distribution of the main superficial vessels on the skull may be examined next. Anterior to the hypoglos­sal nerve, the external carotid gives rise to the lingual artery, which passes anteromedially toward the base of the tongue. The lingual artery is also crossed by the hypoglossal nerve. The external carotid continues as a large vessel and soon gives rise to the facial artery, which passes anteriorly along the ventral margin of the masseter muscle and subdivides into various branches to supply the jaws and facial structures. The external carotid continues dorsally, deep to the mandibular gland. Follow it by dissecting between the ventral parts of the mandibular and parotid glands. It gives rise first to the posterior auricular artery, a fairly large branch that extends dorsally behind the ear, and then the super­ficial temporal artery, a smaller branch, extending dor- sally anterior to the ear. The superficial temporal divides into the anterior auricular artery and transverse facial artery. After if gives off the superficial temporal, the external carotid continues as the maxillary artery, a large vessel that passes into the dorsal part of the mas­seter muscle to supply orbital and palatal regions.

The regions supplied by the arteries discussed in the pre­ceding paragraph are drained by veins that extend mainly parallel to the arteries but with slightly different branch­ing patterns. Return to the external jugular vein and trace it forwards toward the skull. Three large vessels were noted in connection with the beginning of external jugular on page 180. These branches will now be consid­ered in detail. The external jugular is formed by the con­fluence of the maxillary vein and linguofacial vein. The latter extends anteriorly between the two prominent lymph nodes lying ventral to the salivary glands (see page 180). The transverse jugular vein enters the very proximal end of the linguofacial vein, although in some individuals the transverse facial, linguofacial, and maxillary veins appear nearly to branch from the same point. Follow the linguofacial anteriorly. It is formed by the union of the facial vein, which extends along the ventral margin of the masseter muscle, and the lingual vein, which extends ventromedially in draining the mandible, lower lip, and tongue. The maxillary vein extends dorsally deep to the parotid gland. Follow it, dissecting away potions of the gland as necessary, to see the posterior auricular vein,

FIGURE 7.55 Arterial, partial venous system and nerves anterior to the heart of the cat in ventral view.

from behind the ear, entering the maxillary. The latter continues a short distance anterodorsally to receive the superficial temporal vein and then continues deep to the posteroderosal margin of the masseter muscle. The super­ficial temporal receives the anterior auricular vein from in front of the ear and continues anteriorly toward the eye as the transverse facial vein.

Finally, consider the branches of the subclavian arteries and veins (Figures 7.53-7.56). These vessels help supply

FIGURE 7.56 Schematic illustration of the arteries anterior to the heart of the cat in ventral view.

and drain the forelimbs, as well as regions of the neck and thorax. Trace them on the side opposite that on which the forelimb muscles were dissected. For the most part, it is easier to find the arteries and then note the corresponding veins, which run beside them but are not injected.

The subclavian artery and vein pass toward the forelimb laterally, just in front of the first rib. Follow the subclavian artery. Just before it passes out of the thorax, it gives rise to four arteries. Dissect around the artery to find these branches. The internal mammary artery arises from the ventral surface of the subclavian artery and extends pos­teriorly. The left and right internal mammary arteries con­verge toward the ventral midline, and pass along either side of the sternum in parallel with the internal mammary veins, which was noted earlier (see page 196). If you have trouble locating its origin, follow the artery proximally to the subclavian artery from the midventral strip of the thorax. Note that the internal mammary vein empties into the anterior vena cava and not the subclavian vein. The costocervical artery arises from the posterodorsal surface of the subclavian almost opposite to the internal mammary artery. The costocervical is a short trunk that soon branches into two vessels. The highest intercostal artery is the smaller branch. It passes back over the medial surface of the first rib onto the anterior part of the thorax. The other, larger branch is the deep cervical artery, which extends almost directly dorsally to supply deep neck muscles.

The other two arteries, the vertebral and thyrocervical arteries, can be exposed by gently pulling the subclavian posteriorly and carefully dissecting along its anterior surface. The vertebral artery is more medial and passes anteriorly and dorsally. The thyrocervical artery is more lateral. It passes anteriorly deep to the subclavian vein and then for a short distance follows along the dorso­lateral side of the external jugular vein. It gives off a small medial branch toward the thyroid and then passes laterally as the transverse scapular artery, in company with the transverse scapular vein, at about the level of the anterior part of the shoulder.

Just anterior to the first rib, the subclavian artery and vein pass from the thorax into the axilla (armpit) as the axillary artery and vein. These vessels and their branches extend toward the forelimb in company with the complex of nerves termed the brachial plexus, which was examined briefly in Section III, so the vessels require careful dissection. The axillary artery sends out various branches, mainly to surrounding pectoral musculature, before it branches into two large vessels, the brachial artery, which continues onto the medial surface of the brachium, and the subscapular artery, which extends into the musculature toward the anterior part of the shoulder. The axillary vein receives the subscapular vein. Distally it follows the subscapular artery, but it enters the axillary vein more proximally than the origin of the subscapular artery from the axillary artery. The axillary vein continues distally, receiving tributaries from the surrounding musculature, and passes onto the medial surface of the brachium as the brachial vein.

Vessels Posterior to the Diaphragm

The vessels considered here mainly supply and drain the musculature and organs in the posterior part of the body. Trace the posterior vena cava posteriorly from the heart (Figures 7.42, 7.43, 7.45, 7.46, 7.53, and 7.54). It passes through the diaphragm and enters the liver. It receives several hepatic veins from the liver, but does not drain the liver directly. Scrape away some of the liver, just anterior to its quadrate lobe, to expose the veins. The posterior vena cava continues through the liver. It emerges into the abdominopelvic cavity from beneath the caudate lobe of the liver, passes between the left and right kidneys, and continues posteriorly (Figures 7.58 and 7.59). Return to the thoracic aorta and, lifting the left lung, trace it posteriorly (Figure 7.51). It passes through the diaphragm and into the abdominopelvic cavity as the abdominal aorta, and extends posteriorly to the left of the posterior vena cava (Figure 7.58).

Push the digestive tract and spleen to the right, so you can view the abdominal aorta from the left side. Imme­diately on passing through the diaphragm, it gives rise to the celiac artery and then the anterior mesenteric artery, both large, unpaired vessels that mainly supply the viscera (Figure 7.58). With the viscera pushed to the right, these vessels pass directly laterally toward the

FIGURE 7.57 Branches of the common carotid artery, and muscles and nerves of the throat of the cat in ventral view.

right. They will be traced shortly. The veins that drain these structures are part of the hepatic portal system and are also discussed below. Careful dissection will reveal several ganglia along the ventral surface of the aorta between the origins of these arteries. Continue to follow the aorta posteriorly. The next large branches of the aorta are the paired renal arteries. Remove the peri­toneum covering the kidneys, and follow the right and left renal arteries as they pass toward the central part of the medial surface of each kidney. As the right kidney lies slightly anterior to the left kidney, the right renal artery is slightly anterior to the left renal artery. The renal veins (Figures 7.58 and 7.59), of which the left is usually larger, follow the renal arteries.

FIGURE 7.58 Abdominopelvic cavity of the cat showing arteries and veins posterior to the heart, with most of digestive system removed and urinary bladder reflected, in ventral view.

FIGURE 7.59 Schematic illustration of the veins posterior to the heart of the cat in ventral view.

Between the anterior mesenteric and renal arteries, the aorta usually gives rise to slender and paired adrenolumbar arteries, which may also arise from the renal arteries (Figures 7.58 and 7.60). On each side, the adrenolumbar artery supplies and passes the small, nodular adrenal gland. The right adrenal gland lies between the anterior end of the kidney and the vena cava, and the left adrenal gland lies between the kidney and the aorta. Remove the fat and tissue from around the glands to expose them. Lifting the kidneys, follow the adrenolumbar arteries. They continue onto the dorsal wall of the abdominal cavity. The adrenolumbar veins accompany the arteries. They may empty into the poste­rior vena cava or the renal veins (Figures 7.58 and 7.59).

Posterior to the renal arteries, the aorta gives rise to paired gonadal arteries, internal spermatic arteries in the male and ovarian arteries in the female (Figures 7.58, 7.60). In the female they pass almost directly laterally to the ovaries, which lie at the anterior end of each uterine horn, the paired proximal extensions of the uterus (Figure 7.71). In the male, however, the internal spermatic arteries extend posteriorly, through the

FIGURE 7.60 Schematic illustration of the arteries posterior to the heart of the cat in ventral view.

abdominal wall (by way of the inguinal canal) to the scrotum, which contains the testes (Figures 7.58, 7.70). The right ovarian and internal spermatic veins closely follow the corresponding arteries to enter the posterior vena cava. On the left side, however, the prox­imal portions of the artery and vein are further apart because the vein enters the renal vein.

The next aortic branch, the posterior mesenteric artery, is an unpaired vessel arising from the ventral surface of the aorta that helps supply the viscera. Its peripheral dis­tribution is discussed below. Almost immediately poste­rior to the origin of the inferior mesenteric artery, the aorta gives rise to the paired deep circumflex iliac arter­ies. The deep circumflex iliac veins closely follow the arteries to enter the posterior vena cava.

Just beyond these vessels, the aorta gives rise to two large branches, the external iliac arteries, which extend posterolaterally into each hindlimb. The aorta contin­ues as a narrower vessel for a very short distance before giving off the internal iliac arteries, which also extend posterolaterally but are smaller than the external iliacs. Follow the internal iliacs for a short distance to see that they give off branches to the pelvic viscera. Past the origin of the internal iliacs, the aorta continues as the small median sacral artery and then enters the tail as the caudal artery (but you will not look for it).

In contrast to the similar branching patterns of most of the paired arteries and veins of the aorta and posterior vena cava, the patterns of the iliac arteries and veins differ. Near the origin of the external iliac arteries, the posterior vena cava begins with the confluence of two large tributaries, the common iliac veins. Each common iliac vein, in turn, is formed by the confluence of the internal and external iliac veins. The median sacral vein, which accompanies the median sacral artery, usually joins one of the common iliac veins and continues in the tail as the caudal vein.

Return to the external iliac arteries and follow one of them distally. It passes through the abdominal wall and enters the hindlimb as the femoral artery. Just before it passes through the body wall, it gives rise from its medial surface to the deep femoral artery. The latter gives rise to several branches and then passes deep into the medial side of the thigh (see also Figure 7.32). The internal iliac artery mainly supplies muscular and vis­ceral structures in the pelvic canal. Its first branch, the umbilical artery, supplies the urinary bladder. The femoral vein and deep femoral vein empty into the external iliac vein. The umbilical vein usually empties into the internal iliac vein.

Vessels Associated with the Viscera

In this section, the vessels that supply and drain the viscera are examined. The arterial system consists of three vessels, the celiac, anterior mesenteric, and poste­rior mesenteric arteries, and their branches. Their origin from the aorta have already been identified. The struc­tures supplied by these arteries are drained by tributaries that ultimately form the hepatic portal vein, which returns blood to the liver (Figures 7.58, 7.61, and 7.62). The hepatic portal breaks up into capillaries within the liver. These re-collect into several hepatic veins, which then enter the posterior vena cava.

Reflect the viscera to the right, and locate the origins of the celiac and anterior mesenteric arteries as they first arise from the aorta, as it emerges through the diaphragm, and then extend toward the right. The celiac is a short trunk that divides into three branches. Two of these, the hepatic and left gastric arteries, slant anteriorly toward the right in this view. The third, the splenic artery, is the largest and extends almost directly toward the right. You can easily follow the hepatic for about 2 cm in this view, but change perspective to follow it more distally.

Reflect the viscera (including the duodenum and head of the pancreas) to the left, and locate the hepatic portal vein, sitting primarily on the caudate lobe of the liver, and the common bile duct as it extends toward the duo­denum; these structures were exposed earlier (page 191). The hepatic portal is difficult to see if it is not injected. Carefully dissect along the hepatic portal vein, freeing it as much as possible from connective tissue without destroying any of its branches. (In some speci­mens the vein is injected with yellow latex, which greatly facilitates dissection.) In doing so, you should reveal the hepatic artery (Figures 7.61 and 7.63). Ascer­tain that this is indeed the hepatic artery by reflecting the viscera to the right again, gently but firmly grasping the hepatic artery with blunt forceps, and then reflect­ing the viscera to the left again, thus verifying that the gripped vessel is the one you saw from the other view. This method of using forceps to identify a vessel can be used to advantage in many situations.

Follow the hepatic artery anteriorly. Near the anterior margin of the caudate lobe, it usually gives off several branches, three of which can be followed into the lobes of the liver. The fourth, the gastroduodenal artery, follows the common bile duct as it heads toward the duodenum. Trace it until it divides into posteriorly curving and anteriorly curving branches dorsal to the pylorus. The posterior branch, the anterior pancreatico­duodenal artery, passes between the duodenum and pancreas. The anterior branch, the right gastroepiploic artery, passes to the distal part of the greater curvature of the stomach. Follow the right gastroepiploic artery with the duodenum in natural position but with the stomach reflected anteriorly (i.e., so you view its dorsal surface). The arteries are followed closely by corresponding veins. Trace the right gastroepiploic vein and anterior pancre­aticoduodenal vein; their confluence forms the gastro­duodenal vein, which enters the hepatic portal vein.

With the stomach reflected anteriorly, gently pull the tail of the pancreas posteriorly. Dissect away the connective tissue and fat between the pancreas and stomach to reveal a system of arteries and veins. Then, reflect the viscera to the right and grasp the left gastric artery with forceps, and again reflect the stomach anteriorly. Trace the left gastric artery as it passes onto the lesser curvature of the stomach. The left gastric vein accompanies the artery.

The splenic artery passes to the left toward the spleen (verify this by reflecting the viscera to the right and grasping the vessel with forceps). The gastrosplenic vein, which accompanies the splenic artery, is conspicuous even in uninjected specimens. It is formed by the con­fluence of the gastric vein and the splenic vein. Follow the splenic artery and vein. After one or two small branches to the stomach, the vein and artery divide. Follow the vein first, with both the stomach and spleen reflected anteriorly. In this view, one tributary, the ante­rior splenic vein, heads almost directly laterally and drains the left side of the spleen; the other, the posterior splenic vein, passes posterolaterally and drains the right

FIGURE 7.61 Detail of vessels of the viscera, showing liver (reflected) stomach, duodenum, pancreas, and spleen (reflected) of the cat in ventral view.

side of the spleen. The anterior and posterior splenic arteries also follow this pattern, but the right splenic artery lies deep to the vein and is not apparent at first. Trace the left splenic artery and vein into the spleen. Some of their branches will be seen to stretch across to the greater curvature of the stomach. These are the left gastroepiploic arteries and veins.

Work your way back proximally along the gastrosplenic vein. Its confluence with the anterior mesenteric vein, oriented nearly anteroposteriorly, forms the hepatic portal vein. Dissect along the anterior mesenteric vein for about 3 cm. With the viscera reflected to the right, trace the anterior mesenteric artery as it angles posteriorly to the right. Note the anterior mesenteric vein converging toward the artery. Continue to expose the anterior mesenteric artery. You will need to move through the coils of the intestines individually and tear the mesentery binding the coils together. As the artery and vein extend distally, they give off numerous branches, which mainly supply and drain the jejunum, ileum, cecum, and proxi­mal portion of the colon (Figure 7.49).

FIGURE 7.62 Schematic illustration of the hepatic portal system of the cat in ventral view.

Two proximal branches of the anterior mesenteric artery should be traced. They often arise in close prox­imity, and either may have the more proximal origin. The posterior pancreaticoduodenal artery extends to the distal part of the duodenum and head of the pancreas. It passes anteriorly and anastomoses with the anterior pancreaticoduodenal artery. If you have trouble tracing the posterior pancreaticoduodenal artery from the ante­rior mesenteric, begin by tracing the anterior pancreati­coduodenal artery posteriorly, and then follow the posterior pancreaticoduodenal artery to the anterior mesenteric artery. The artery is accompanied by the pos­terior pancreaticoduodenal vein, which empties into the anterior mesenteric vein.

The other branch of the anterior mesenteric artery is the middle colic artery. It gives off various branches, but its main part continues posteriorly along the medial side of the descending colon. The vein that accompanies the artery proximally is the posterior mesenteric vein, which empties into the anterior mesenteric vein near the entrance of the posterior pancreaticoduodenal vein.

Next, trace the posterior mesenteric artery. It is the smallest and least complexly branched of the arteries that supply the viscera. Usually, the posterior mesenteric artery forms a short trunk that branches into the left colic artery and the anterior rectal artery. The left colic passes anteriorly on the surface of the descending colon and anastomoses with the middle colic artery. The anterior rectal artery passes posteriorly to supply

FIGURE 7.63 Schematic illustration of the visceral arterial system of the cat in ventral view.

the distal end of the colon and the rectum. These arter­ies are accompanied by the posterior continuation of the posterior mesenteric vein, which sequentially becomes the left colic vein and the anterior rectal vein.

Key Terms: Cardiovascular System

abdominal aorta adrenal gland adrenolumbar artery adrenolumbar vein anterior auricular artery anterior auricular vein anterior mesenteric artery

anterior mesenteric vein anterior

pancreaticoduodenal artery

anterior pancreaticoduodenal vein

anterior rectal artery

anterior rectal vein anterior splenic artery anterior splenic vein anterior vena cava aorta aortic arch apex of heart ascending pharyngeal artery atrium (plur., atria) auricle axillary artery axillary vein azygos vein Continues

FIGURE 7.65 Flow chart diagram of the venous system anterior to the heart of the cat.

FIGURE 7.66 Flow chart diagram of the arterial system posterior to the heart of the cat.

FIGURE 7.67 Flow chart diagram of the venous system posterior to the heart of the cat. *May instead enter the posterior vena cava directly. **May instead enter the left common iliac vein.

base of heart brachial artery brachial vein brachiocephalic artery brachiocephalic vein caudal artery caudal vein celiac artery cephalic vein common carotid artery common iliac vein coronary artery coronary sulcus coronary vein (cardiac vein)

costocervical artery costocervical vein costocervical + vertebral trunk

deep cervical artery deep circumflex iliac artery

deep circumflex iliac vein deep femoral artery deep femoral vein external carotid artery external iliac artery external iliac vein external jugular vein facial artery facial vein femoral artery femoral vein gastroduodenal artery gastroduodenal vein gastroepiploic vein gastrosplenic vein heart hepatic artery hepatic portal system hepatic portal vein hepatic vein highest intercostal arteries

highest intercostal veins hypoglossal nerve intercostal artery intercostal vein internal carotid artery internal carotid ligament internal iliac artery internal iliac vein internal jugular vein internal mammary artery

internal mammary vein internal spermatic artery internal spermatic vein interventricular groove left colic artery left colic vein left gastric artery left gastric vein left gastroepiploic artery left gastroepiploic vein ligamentum arteriosum lingual artery lingual vein linguofacial vein

(anterior facial vein) maxillary artery maxillary vein (posterior facial vein)

median sacral artery median sacral vein middle colic artery occipital artery ovarian artery ovarian vein pericardial cavity pericardium phrenic nerve posterior auricular artery

posterior mesenteric artery

posterior mesenteric vein

posterior pancreaticoduodenal artery

posterior pancreaticoduodenal vein

posterior splenic artery posterior splenic vein posterior vena cava pulmonary arteries pulmonary trunk pulmonary vein renal artery renal vein right gastroepiploic artery

splenic artery splenic vein subclavian artery subclavian vein subscapular artery