THE LANGUAGE OF ANATOMY
Anatomical language must be precise and unambiguous. In an ideal world each term would have a single meaning, each structure a single name. Unhappily, there has long been an alarming superfluity of terms and much inconsistency in their use.
In the hope of reducing this confusion, an internationally agreed-on vocabu- lary—Nomina Anatomica Veterinaria (NAV)—was introduced in 1968 and has since obtained wide acceptance. It is revised periodically, most recently in 1994, and we have tried to use it consistently throughout this work. Occasionally, we have included a second, older, and unofficial alternative when such a term appears to be so deeply rooted in clinical usage that it is unlikely to be eliminated by edict. The terms of the NAV are in Latin, but it is permissible to translate them into vernacular equivalents and is usual in English-speaking countries to do so. We have given preference to translations that so closely resemble the original Latin that the equivalence is immediately recognizable. We therefore give the Latin name only when the translation could be in doubt. No handy English equivalents exist for some official terms; in these cases it is conventional to use the Latin terms, perhaps in abbreviated form, as though they were English words or phrases. The resulting mixture of languages is jarring but not easily avoided, particularly when describing groups of muscles. The names, whether in Latin or in English, are intended to be informative and an aid to comprehension. It is more sensible to look up any word whose meaning is not self- evident in an anatomical or medical dictionary than to use it “parrot fashion.”The names that are given to particular structures will be encountered gradually, but the terms that indicate position and direction must be mastered at once. These official terms are more precise than the common alternatives because they retain their relevance regardless of the actual posture of the subject.
They are defined in the following list, and their use is illustrated in Figure 1-1. We have not thought it sensible to use them pedantically when there is no reasonable prospect of misunderstanding. When we use common terms (above, behind, and so forth), we always have in mind a standard anatomical position, which, for a quadruped, is that in which the animal stands square and alert. This differs from the human anatomical position, and difficulties with terminology will be encountered when books are consulted that refer primarily to the human body. Medical anatomists make much use of the terms anterior and posterior, superior and inferior, all of which have very different connotations when applied to quadrupeds. These terms are therefore best avoided, except for a few specific applications to the anatomy of the head.The principal recommended terms of position and direction are arranged in pairs, and it should be emphasized that they refer to relative, not absolute, position. Most of these adjectives form corresponding adverbs by the addition of the suffix -ly.
Dorsal structures (or positions) lie toward the back (dorsum) of the trunk or, by extension, toward the corresponding surface of the head or tail.
Ventral structures lie toward the belly (venter) or the corresponding surface of the head or tail.
Cranial structures lie toward the head (cranium, literally skull), caudal ones toward the tail (cauda). Within the head, structures toward the muzzle (rostrum) are said to be rostral; caudal remains appropriate.
Medial structures lie toward the median plane (medianus, in the middle) that divides the body into symmetrical right and left “halves.”
Lateral structures lie toward the side (latus, flank) of the animal.
Different conventions apply within the limbs. Structures that lie toward the junction with the body are proximal (proximus, near), whereas those at a greater distance are distal (distantia, distance). Within the proximal part of the limb (which is defined for this purpose as extending to the proximal limit of the carpus [wrist] or tarsus [hock, ankle]), structures that lie toward the “front” are said to be cranial, those that lie toward the “rear,” caudal.
Within the remaining distal part of the limb, structures toward the “front” are dorsal (dorsum, back of the hand), and those toward the “rear” are palmar (palma, palm of the hand) in the forelimb or plantar (planta, sole of the foot) in the hindlimb. Additional terms may be applied to the anatomy of the digits. Axial structures lie close to the axis of a central digit, close to the axis of the limb if this passes between two digits; abaxial (ab, away from) positions are at a distance from the reference axis.The terms external and internal, superficial and deep (profundus) hardly require explanation or definition.
Sometimes it is necessary to refer to a section through the body or a part of it (see Figure 1-1). The median plane divides the body into symmetrical right and left halves. Any plane parallel to this is a sagittal plane, and those close to the median are sometimes termed paramedian planes. A dorsal plane sections the trunk or other part parallel to the dorsal surface. A transverse plane
Figure 1-1 Directional terms and planes of the animal body. The stippled areas represent the carpus and tarsus on forelimbs and hindlimbs, respectively.
transects the trunk, head, limb, or other appendage perpendicular to its own long axis.
AN INTRODUCTION TO REGIONAL ANATOMY
Although the first nine chapters that follow deal with systematic anatomy, those readers who are about to begin a laboratory course will find that they require an elementary knowledge of several systems at once. It is the principal purpose of the remainder of this chapter to supply that background. However, devoting some attention to the live animal also has benefits.