40 Anatomy of the Rabbit. 



teria; (c) platelets, minute nucleate amoeboid cells found in the 

 blood stream. 



In all multicellular animals the tissues are removed more or less 

 extensively from the surfaces of absorption and excretion. Blood 

 and lymph are the media through which tissue metabolism is 

 maintained, and the vascular system is the mechanical means by 

 which the continuous circulation of fluid is brought about. The 

 composition of the blood varies from time to time according to the 

 individual fuactions performed. Oxygen and food materials are 

 carried to the tissues. Carbon dioxide and waste materials of 

 other kinds are carried to organs from which they can be excreted. 

 Blood, however, has been shown to vary in composition in diflFerent 

 species of animals, and to be chemically homologous in related ones; 

 while it possesses immunizing properties towards bacterial diseases, 

 also differing in different species and individuals. 



TERMINOLOGY. 



In special or descriptive anatomy it is necessary to employ an 

 extensive system of terminology in order that the various structures 

 of the body may be individually designated, classified, and referred 

 to their respective positions. The terms used for this purpose may 

 be classified into four groups, as follows: (i) general terms — 

 those included in the names of parts, but applicable in themselves 

 to similar structures (arteries, nerves, etc.) in various parts of the 

 body; (2) specific terms or names of parts; (3) regional 

 terms — ^those defining areas (topographic) ; and (4) terms of 

 orientation. 



Although few in number, the terms of orientation may be 

 regarded as the most generally useful terms of descriptive anatomy. 

 This is because they are based on very general relations of the body 

 and are therefore of wide application. For this reason they are 

 here selected for definition to the exclusion of others of a more 

 restricting or individualizing kind. 



In all vertebrates we may recognize a longitudinal axis, 

 corresponding, in general, to the line formed by the vertebral 

 column. In the usual or prone position of the body this axis is 

 horizontal. The uppermost surface is then described as dorsal, 



