18 INTRODUCTION 
apparatus which are similar in origin and structure and are associated in the per- 
formance of certain functions. The divisions of systematic anatomy are: 
1. Osteology, the description of the Skeleton. 
2. Arthrology, the description of the Joints. 
3. Myology, the description of the Muscles and accessory structures. 
4. Splanchnology, the description of the Viscera. This includes the following 
subdivisions: 
(1) Digestive System 
(2) Respiratory System 
(3) Urogenital System 
(a) Urimary Organs 
(b) Genital Organs 
5. Angiology, the description of the Organs of Circulation 
6. Neurology, the description of the Nervous System 
7. Aisthesiology, the description of the Sense Organs and Common Integu- 
ment 
The term topographic anatomy designates the methods by which the relative 
positions of the various parts of the body are accurately determined. It presup- 
poses a fair working knowledge of systematic anatomy. 
Descriptive Terms.—In order to indicate precisely the position and direction 
of parts of the body, certain descriptive terms are employed, and must be under- 
stood at the outset. In the explanation of these terms it is assumed here that 
they apply to a quadruped such as the horse in the ordinary standing position. 
The surface directed toward the plane of support (the ground) is termed ventral 
(or inferior), and the opposite surface is dorsal (or superior); the relations of parts in 
this direction are named accordingly. The longitudinal median plane divides the 
body into similar halves. A structure or surface which is nearer than another to the 
median plane is medial (or internal) to it, and an object or surface which is further 
than another from the median plane is lateral (or external) to it. Planes parallel 
to the median plane are sagittal. Transverse or segmental planes cut the long axis 
of the body perpendicular to the median plane, or an organ or limb at right angles 
to its long axis. A frontal plane is perpendicular to the median and transverse 
planes. The term is also used with reference to parts of the limbs or various organs 
in asimilar sense. The head end of the body is termed anterior or cranial; and the 
tail end posterior or caudal; relations of structures with regard to the longitudinal 
axis of the body are designated accordingly. With respect to parts of the head, 
the corresponding terms are oral and aboral. Certain terms are used in a special 
sense as applied to the limbs. Proximal and distal express relative distances of 
parts from the long axis of the body. The anterior face of the thoracic limb from 
the elbow downward is termed dorsal, and the opposite face volar. In the corre- 
sponding part of the pelvic limb the terms are dorsal and plantar respectively. In 
the same regions radial and ulnar (thoracic limb), tibial and fibular (pelvic limb), 
may be used to designate that side of the extremity on which the corresponding 
bone is situated; they are therefore equivalent respectively to medial and lateral 
in the animals with which we are concerned. The terms superficial (superficialis) 
and deep (profundus) are useful to indicate relative distances of parts from the 
surface of the body. 
It is evidently advantageous to employ terms which are as far as possible independent of 
the position of the body in space and capable of general application, e. g., dorsal, ventral, proximal, 
etc. It is also desirable that the terms internal and external be reserved to indicate relations of 
depth in cavities or organs, and medial and lateral to designate relations to the median plane. 
Such terms are coming into more extensive use In human and veterinary anatomy, but the older 
nomenclature is very firmly established and cannot well be discarded at once and entirely. To 
facilitate the transition, a table of the older and more recent terms is given below; the recent 
terms are in the first column and the older equivalents in the second. 
