ON THE VERTEBRATE SKELETON'. 249 



Although my investigations of the fundamental type of the vertebrate 

 skeleton were first made upon the class of fishes, where vegetative uniformity 

 or irrelative repetition most prevails, and where, therefore, the type is least 

 obscured by the modification of one part in mutual subserviency with an- 

 other, I soon found that I should be led astray by confining my observations 

 to fishes, and by borrowing my illustrations from that class. Comparison 

 of the piscine skeleton with those of the higher animals demonstrates that 

 the natural arrangement of the parts of the endoskeleton is in a series of 

 segments succeeding each other in the axis of the body. These segments are 

 not, indeed, composed of the same number of bones in any class or throughout 

 any individual animal. But certain parts of each segment do maintain such 

 constancy in their existence, relation, position, and offices, as to enforce the 

 conviction that they are homologous parts, both in the constituent series of the 

 same individual skeleton, and throughout the series of vertebrate animals. 

 For each of these primary segments of the skeleton I retain the term ' verte- 

 bra'; but with as little reference to its primary signification, as a part 

 specially adapted for rotatory motion, as when the comparative anatomist 

 speaks of a sacral vertebra. The word may, however, seem to the anthro- 

 potomist to be used in a different or more extended sense than that in which 

 it is usually understood ; yet he is himself, unconsciously perhaps, in the 

 habit of including in certain vertebras of the human body, elements which he 

 excludes from the idea in other natural segments of the same kind, influenced 

 by differences of proportion and coalescence, which are the most variable 

 characters of a bone. Thus the rib of a cervical vertebra is the 'processus 

 transversus perforatus,' or the ' radix anticus processus transversi vertebras 

 colli ' *: whilst in the chest, it is ' costa,' or ' pars ossea costae.' But the ulna 

 is still an ulna in the horse, although it be small and anchylosed to the radius. 

 The osteology of man, therefore, cannot be fully or rightly understood 

 until the type of which it is a modification is known, and the first step to 

 this knowledge is the determination of the vertebral segments, or natural 

 groups of bones, of which the myelencephalous skeleton consists. 



I define a vertebra, as one of those segments of the endoskeleton which con- 

 stitute the axis of the body, and the protecting canals of the nervous and 

 vascular trunks : such a segment may also support diverging appendages. 

 Exclusive of these, it consists, in its typical completeness, of the following 

 elements and parts : — 



Fig. 14. 



neural spine. 



Jl|» - neurapophysis. 



C -—J O ', "CJijTRu ran Q f™ -7> .- plpui -apophysis , 

 parapophysis. •-'' %* © /# 



If ""-■ haemal spine. 



Ideal typical vertebra. 



* Soemmerring, De Corporis Humani Fabrica, 1794, i. p. 239. 

 1846. 



