82 ARCHETYPE OF THE SK:ELET0]S". 



e. g. the median liorn supported by the nasal^ spine, 15, in 

 the rhinoceros ; the pair of lateral horns developed from 

 the frontal spine, 11, in most ruminants; the median folds, 

 Di, Dii, above the neural spines, one or more in number, 

 constituting the " dorsal" fin or fins in fishes and cetaceans, 

 and the dorsal hump or humps in the buffaloes and camels ; 

 similar folds are sometimes developed at the end of the 

 tail, forming a "caudal" fin, C, and beneath the hoemal 

 spines, constituting the " anal" fin or fins. A, of fishes. 



The different elements of the primary segments are 

 distinguished by peculiar markings: — 



The neurapophyses by diagonal lines, thus — llljj 



The diapophyses by vertical lines — 



The parapophyses by horizontal lines — :==: 



The centrum by decussating horizontal and vertical lines - ^ 



The pleurapophyses by diagonal lines — 



The appendages by dots — 



The neural spines and hsemal spines are left blank. 



In certain segments, the elements are also specified by 

 the initials of their names : — 



ns is the neural spine. 



n is the neurapophysis. 



pi is the pleurapophysis. 



c is the centrum. 



h is the hosmapophysis, also indicated by the Nos. 21, 20, 44, 



52, 58, G3, 64. 

 hs is the haemal spine. 

 a is the appendage. 



The centrum is the most constant vertebral element as 

 to its existence, but not as to its ossification. There are 

 some living fishes — and formerly there were many, now 



