PRIMARY DIVISIONS OF THE BODY. 29 



Practical Application of the Foregoing Considerations in the 

 Designation of Some Parts, and in the Indication of their Relative 

 Position and Direction. 



54. The Primary Divisions of the Body. Soma and Mem- 

 bra. The entire body of a normal and complete Vertebrate presents a 

 principal axial portion, and an appendicular portion, the arms and legs, 

 which may be spoken of, collectively, as the limbs or membra. 



Neither the classical nor the vernacular terms for these divisions have 

 been used with desirable exactitude. With the ancients, corpus might 

 signify either the entire body, or the trunk as distinguished from the head, 

 while the English body may refer to either the whole body in distinction 

 from the mind, the axial part in distinction from the appendicular part, or 

 the principal portion of the former in distinction from the head and the tail. 

 Truncus usually meant the body apart from the limbs, but the head and the 

 trunk are sometimes spoken of as distinct regions. 



In view of this lack of discrimination we venture to suggest that the 

 entire physical part of an animal be called the corpus or body ; that triincus 

 and trunk be applied only to that part of the axial portion which intervenes 

 between the neck and the tail ; and that the entire axial portion, including 

 head, neck, trunk and tail be denominated the soma. 



It is true that the Greek OU\LO, was generally equivalent to the Latin 

 corpus, and that many of its derivatives and compounds refer to the entire 

 organism ; but the term somatome was proposed by Goodsir to indicate a 

 vertebral segment, of which the limbs are merely occasional components. 

 Somite and somatopleure are used by Balfour, A, II, 3, 141. 



The undesirability of the introduction of a somewhat unfamiliar term is 

 fully admitted. It is probable, however, that it need not be employed very often. 



55. Figure 2 is a diagram of the dorsal aspect of the cat, intended to 

 illustrate certain very general features of it or of any other vertebrate 

 provided with two pairs of limbs. 



The outline of the soma is elliptical, the larger end corresponding to the 

 head, and the smaller with the tail. 



The arms and legs are represented as lateral appendages projecting at 

 right angles with the longitudinal somatic axis, or meson. 



Each limb has an attached or proximal end, and a free or distal end. 



The right and left sides of the entire body are antitropic or symmetrical 

 with each ofyer ; that is, they are reversed repetitions of one another in 

 opposite directions. 



56. Beginners in Anatomy are sometimes confused by the fact that, 

 with some figures, the right is at their own right, while with others the 

 right of the figure is upon their left. 



This confusion may be avoided by a preliminary exercise with a familiar 

 object : 



