ON THE STRUCTURE AND DEVELOPMENT OF THE VERTE- 

 BRAL COLUMN OF AMIA. O. P. HAY, PH. D. 



I. DESCRIPTION OF THE GROSS STRUCTURE OF THE VERTEBRAL 



COLUMN. 



For our knowledge of the vertebral column of the fish Amia we 

 are indebted to a considerable number of writers, whose works will 

 be found in the list at the end of this paper. Their views, so far as 

 they concern our present purpose, will receive consideration as our 

 discussion proceeds. 



In again calling attention to the spinal column of this fish, we 

 must first of all consider a peculiarity which has struck all investiga- 

 tors, and which distinguishes this species from all other living osse- 

 ous fishes. This peculiarity consists in the possession, throughout the 

 greater portion of the tail region, of apparently twice as many verte- 

 bral bodies as there are myomeres and neural and haemal arches. 

 Franque (26) appears to have been the first to remark on this struc- 

 tural feature of this fish. He regarded those vertebral centra which 

 are devoid of upper and lower arches as intercalated vertebrae 

 similar to those which are found in certain sharks and rays. He says: 

 ' Sunt igitur corpora vertebrarum inter vertebras intercalata." 

 He refers to the fact that among the Rays Rhinobatus has intercalated 

 vertebrae, while among the Squali Sphyrna malleus has intercalated 

 superior arches. Almost all other writers who have dealt with the 

 subject have adopted the same interpretation, while it is the express 

 purpose of a recent paper by Ludwig Schmidt (56) to establish this 

 view. On the other hand, Dr. G. Baur (9) and Dr. Carl Zittel (60) 

 hold that the two segments of the vertebral column which are found 

 in each of the myomeres in question are "centra" and " intercen- 

 tra," (pleurocentra* and hypocentra.), corresponding to those ele- 

 ments which together make up a vertebral body in some of the Stego- 

 cephali. 



I signify my acceptance of the opinion that the whole vertebral 

 column of the ancestors of Amia was composed, in each myomere, of 



*The term centrum has long been in, use to distinguish the principal portion of the vertebra 

 independently ot any theory concerning its origin and composition. To apply now this term to dis. 

 tinguishone of the elements that may enter into the construction of a vertebral body would intro- 

 duce confusion. I prefer therefore to employ in this paper pleurocentrum and fiypocentrum to des- 

 ignate the elements of the body. 



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