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) Urinary Organs 

 (h) Genital Organs 



5. Angiology, the description of the Organs of Circulation 



6. Neurology, the description of the Nervous System 



7. ^Esthesiology, 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 a similar 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. In the case of the limbs, a frontal 

 plane is at right angles to the transverse plane and the long axis of the segment 

 involved. 



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 himnan and veterinary anatomy, but the older 

 nomenclature is very firmly established and cannot well be discarded at once and entirely. To 

 facihtate 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. 



