ON THE VERTEBRATE SKELETON. 251 



To the question why I should have invented new names when Geoffroy St. 

 Hilaire had already proposed others for the vertebral elements, I can only re- 

 peat the regret with which I found myself compelled to that invidious step, 

 after having arrived at the conviction, that the learned Parisian Professor had 

 sometimes applied the same term to two distinct elements, and sometimes 

 two distinct names to one and the same element : and I am glad to be able to 

 cite the authority of Cuvier for the propriety and advantage of such a step. 

 His words are in reference to an analogous case, " Donner a un mot connu un 

 sens nouveau est toujours un procede dangereux, et, si Ton avoit besoin 

 d'exprimer une idee nouvelle, il vaudroit encore mieux inventer un nouveau 

 terme, que d'en detourner ainsi un ancien *." Now there is scarcely one term 

 in the first column in Table II. which is synonymous with its opposite in the 

 second column, or which expresses exactly the same idea ; and the discrepancy 

 becomes greater in regard to the terms applied to the vertebral elements of the 

 head, in columns 1 and 5 of Tablelll. The respective concordance of the views 

 of the vertebral archetype entertained by Geoffroy and myself with Nature will 

 be determined and judged of by succeeding impartial and original observers. 



With regard to the term cycUal, " de kvkXos, cercle, pour rappeler sa 

 forme annulaire, permanentes chez les premiers," (Articulata, Dermoverte- 

 bres, Geoff.) " et, au contraire, non perseverante chez les derniers " (Verte- 

 brata, Hauts-vertebres, Geoff.), it is understood by its author to apply to the 

 annular segment of the crust of the insect, as well as to the ' centrum ' of the 

 endoskeletal vertebra. Geoffroy 's primary division of the parts of a vertebra 

 is into the centre or nucleus (noyau) and the lateral branches. The upper 

 ' branches laterales ' or ' periaux ' are equivalent to my neurapophyses and 

 also to my neural spine, in fishes : the lower lateral branches or ' paraaux ' are 

 sometimes free and floating f, when they answer to my ' pleurapophyses '; 

 but they are sometimes so united as to form a canal, when they answer 

 to my ' parapophyses ' in the tail of fishes J, and to my ' hsemapophyses ' in 

 the tail of cetaceans. Geoffroy supposed, for example, that the haemal canal 

 in the tail in all fishes was formed by the ribs, bent down and anchylosed 

 at both ends§, and that the haemal canal in the tail of the crocodile and 

 whale was constituted by a like metamorphosis of the same vertebral elements. 

 He, also, argued that, as the small spinal chord of fishes did not demand 

 so great a development in breadth of the neurapophyses, they were permitted 

 to attain to unusual length ; and that, coalescing together, they thus consti- 

 tuted not only the neural arch but the neural spine, to which latter, therefore, 

 he extended the name ' perial ' ; whilst to the corresponding part in mammals 

 he gives the name of ' epial '. But, again, in fishes, he calls the dermal 

 spines developed in the embryonic median fold of integument which is meta- 

 morphosed into the dorsal fins, 'epiaux' ; and the corresponding dermal spines 

 of the ventral fin ' cataaux.' The lepidosiren, however, manifests the neural 

 spine distinct from both the neurapophyses below and the dermo-neural spine 

 above : and such neural spine is unequivocally homologous with the anchy- 

 losed neural spine in osseous fishes ||. It is quite in harmony with the position 

 of the class of fishes at the bottom of the vertebrate scale that they should 

 present a greater degree of calcification of the parts belonging to the same 

 category of the skeletal system as the shells and crusts of the invertebrates : 

 hence it is that whilst the median dermal fins of the marine mammalia have 



* Memoires du Museum, t. xx. p. 123. 



t As they are illustrated in the abdominal vertebra of the fish figured by Geoffroy in the 

 ' Memoires du Museum,' t. ix. (1822), pi. 5, fig. 4, o. J lb. fig. 2, o o. 



§ This occurs as an exceptional condition, in the lepidosteus, and perhaps in lepidosiren. 

 Ii Linn. Trans, vol. xviii. p. 23, fig. 4, c, d. 



s 2 



