VERTEBRAL COLUMN OF FISHES. 



65 



of fishes contained in the " Le5ons d' Anatomic Compai'ce," * counts 

 the anchylosed vertebras of the caudal fin as one, and so assigns seven- 

 teen vertebra? to the Sun-fish. I find but sixteen according 

 22 Iil\ to the vertebral centres, eight abdominal, and eight caudal : 

 but if we count the neural spines, we have then twelve 

 caudal vertebras ; the spines of the last five being driven, as 

 it were, by the extreme contraction of their anchylosed 

 bodies, to rest their bases upon the back part of the seventh 

 or last upright neural spine. In the Conger there are 162 

 vertebrae, in the Ophidium 204, and in the Gymnotus 236 

 vertebrae ; but even this number is surpassed by some of the 

 plagiostomous fishes. Nor are the extremities of the ver- 

 tebral column the only regions where anchylosis of the ver- 

 tebrae takes place. Hunter had preserved this specimen of 

 confluence of the first two vertebrae of the post-abdominal 

 or caudal region in a large flat-fish (probably Rhornbus, 

 Jig. 22.), forming a true sacrum. In the Halibut {Hippo- 

 glossiis) the parapophyses of the cori'esponding vertebrae, 

 with those of the last abdominal, are similarly united, 

 though the bodies remain distinct. In Loricaria both the 

 upper and lower arches of a considerable part of the caudal 

 region are blended together into an inflexible sacrum ; but, 

 as a general rule, there exists no such impediment to the 

 lateral inflections of the tail in the present class. 



Although the vertebrae maintain a considerable sameness 

 of form in the same fish, they vary much in diflferent 

 species. The bodies are commonly subcylindrical ; as deep, 

 but not so broad, as they are long ; more or less constricted 

 in the middle, in some to such a degree as to present an 

 hour-glass figure. In the Spinachorhinus they are extremely 

 short ; in the Fistularia extremely long ; in the Tetrodon 

 they are much compressed ; in the Platycephalus they are 

 Anchylosed more depressed ; in the tail of the Tunny the entire ver- 

 caiuiai ver- tcbra is cubical, with the ends hollowed as usual, but the 

 sarniin.'of a four other sidcs flat, the upper and lower ones being formed, 

 in the connected scries, by the neural and hasmal arches of 

 the vertebra in advance, flattened down and, as it wore, pressed 

 into cavities on the upper and under surfaces, of the centrum of the 

 next vertebra ; so that the series is naturally locked together in the 

 dried skeleton ; and tliese ai'ches cover not the neural and haemal 

 canals of their own, but of the succeeding, centrum. 



The principle of vegetative repetition is manifested, in osseous 



* Ed. 1836, torn. i. p. 229. 

 VOL. II. F 



