DIVISION I. 



SYSTEMATIC OK DESCRIPTIVE ANATOMY. 



SYSTEMATIC or Descriptive Anatomy embraces the consideration of the 

 organs of the body in an order arranged according to their nature and con- 

 nections. It is called Systematic in opposition to Topographic or Demon- 

 strative Anatomy, in which the various dissimilar organs found in each 

 region are described together, and which is particularly adapted for the 

 study of the relative position of parts. 



The organs and parts of the body may be regarded from two distinct 

 points of view, the Physiological and the Morphological. 



Viewed in their physiological aspect, they form a series of instruments 

 fitted for the accomplishment of particular purposes. Thus, for example, the 

 bones form levers, which are moved by the muscles ; and the combinations 

 of these in the hand are fitted for grasping, while tho^e of the foot are 

 adapted for walking. 



Considered apart from the functions of its organs, the human body, as 

 well as all other organisms, exhibits a regular plan in its construction, to 

 investigate the nature of which is the object of Morphological Anatomy. 

 That plan cannot be competently examined except with the aids furnished 

 by the study of Development and Comparative Anatomy. One of the most 

 general facts connected with the plan of construction of the human body is 

 its segmented nature, similar sets of parts being placed in succession, so that 

 the line of their series forms the long axis of the body, and parts found in 

 one segment or member of the series correspond, often very distinctly, to 

 parts in other segments. 



The segmented plan is that on which are constructed not only vertebrate animals, 

 or all those which are possessed of a vertebral column, but also the higher invertebrate 

 classes. It is most manifestly displayed in the class articulata, in some of which 

 nearly the whole body is composed of a chain of precisely similar segments; while in 

 others the segments are fused together in groups, so as to form more complicated 

 structures. In the human body the appearance of segmentation is seen most con- 

 spicuously in the osseous system ; it likewise pervades the nervous system, and is 

 observable in some other structures. The trunk of the body is formed by a series 

 of segments, indistinguishably blended together in some of the systems, but distinct 

 in others; while the limbs are rather to be regarded as lateral outgrowths connected 

 with a certain number of segments. Such segments of the body, may be named 

 vertebral segment*, or, as Goodsir has suggested, somatomes j and to distinguish 

 sections of the skeleton, the nervous, muscular, or other systems, the terms sderotome, 

 weitrotome, myotomc, &c , proposed by the same author, may sometimes be con- 

 veniently employed. 



