18 VETERINARY ANATOMY apparatus which are similar in origin and structure and are associated in the per- formance of certain functions. The divisions of systematic anatomy are: . Osteology . Arthrology . Myology . Splanchnology (1) Digestive System (2) Respiratory System (3) Urogenital System (a) Urinary Organs (b) Genital Organs . Angiology . Neurology . Aesthesiology (1) Sense Organs (2) Common Integument. 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 inferior or ventral, and the opposite surface is superior or dorsal; 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 internal or medial to it, and an object or surface which is further than another from the median plane is external or lateral 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 head end of the body is termed anterior, cephalic, or cranial ; and the tail cm! posterior or caudal; relations of structures with regard to the longitudinal axis of the body are designated accordingly. Certain terms are used in a special sense as applied to the limbs. Proximal and distal express relative distances of parts from the axis of the body. The anterior face of the thoracic limb from the elbow downward is also 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 internal or medial and external or lateral in the animals with which we are concerned. 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, c. 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.
