610 



VERTEBRATA. 



(1627.) A perfect or typical skeleton must therefore be supposed to 

 consist of all the before-named portions : namely, 1, the cranial and 

 spinal vertebrae ; 2, the face ; 3, an elaborately-formed hyoid frame- 

 work ; 4, the ribs ; 5, a sternal system of bones, constituting, in con- 

 junction with some of the ribs, a thorax ; and 6, of four locomotive 

 extremities, made up of the parts above enumerated as entering into 

 their composition. Seldom, indeed, is it that the student will find even 

 the majority of these portions of the osseous apparatus coexistent in the 

 same skeleton ; but, whatever forms of animals may hereafter present 

 themselves for investigation, let the above description be taken as a 

 general standard of comparison, and let all variations from it be con- 

 sidered as modifications of one grand and general type. 



(1628.) We must, however, proceed one step further in this our pre- 

 paratory analysis of the skeleton, and, instead of regarding the indi- 

 vidual pieces of the osseous framework of an adult animal as so many 

 simple bones, be prepared to find them resolvable into several distinct 

 parts or elements, all or only a part of which may be developed in any 

 given portion of the osseous system. 



(1629.) In order to simplify as much as possible this important sub- 

 ject, we will select, first, what is generally considered as a single bon# 

 one of the most complex vertebrae of a Fish for instance and examine its 

 real composition. 



(1630.) This bone (fig. 306, A) is found to consist of a central por- 

 tion (a), and of sundry 

 processes derived there- 

 from, some of which the 

 younger student of human 

 anatomy would at once 

 be able to call by their 

 appropriate names. To 

 the body of the bone (a) he 

 finds appended the arch 

 (6) which encloses the 

 spinal cord, surmounted 

 by its spinous process (c), 

 and with equal facility 

 he recognizes in the la- 

 teral processes (d d) the 

 analogues of the transverse processes of the human spine ; but here his 

 knowledge fails him, inasmuch as he finds another arch (e) formed 

 beneath the body of the bone, and moreover an inferior spinous process 

 (g), neither of which have any representatives in the human body. 



(1631.) It is evident, therefore, that the human vertebrae are imper- 

 fectly-developed bones, and do not possess all the parts or elements 

 met with in the corresponding portion of the skeleton of a Fish. 



Fig. 306. 



Elements of a vertebra. 



