OCT. r&95. VERTEBRAL COLUMN OF AMIA HAY 47 



each side of the notochord, and from these the bone extends around 

 it, so as finally to form a ring. From the ring the bone spreads up- 

 ward on the upper arches. 



Goette (32) found in Bombinator a continuous cartilaginous band 

 along the upper side of the notochord, distinct from the bases of the 

 arches. Ossification begins in this band by the appearance, sometimes 

 at least, of lateral centers beneath the bases of the arches. These 

 at length form bony rings. Between them the cartilages develop 

 into intervertebral cartilages, which become cross-segmented and 

 form the epiphyses of the vertebral centra. 



Hasse (36) regards the vertebral centra of the Anura as being 

 composed principally of the bases of the upper arches. In the case 

 of the Urodela, Hasse (35) holds that the intervertebral cartilages lie 

 ^between the two sheaths of the notochord; while the ring of bone 

 "which forms the earliest rudiment of the centrum arises in the elas- 

 tic a, first of all on the lower side. Spreading fore and aft these ver- 

 tebral centra come to enclose the intervertebral cartilages in their 

 concave ends. Later, the cartilages divide, and a portion of each is 

 distributed to each of the two enclosing vertebrae. 



On the side of the palaeontologists, von Meyer (47, p. 95, seq.) y 

 accepting the view that the vertebral centrum originates as a ring 

 independently of the arches, concludes that in such forms as Archego- 

 saurus the vertebral column is in an embryonic condition, and that 

 there are no centra present. 



As already stated, Prof. Cope regards the vertebrae of the mod- 

 ern amphibians, like that of the Teleostomi, as being derived wholly 

 from the hypocentra. 



On page 123 of this paper I have called attention to the inter- 

 vertebral rings of cartilage which, in a certain stage of development, 

 surround the notochord of Lepisosteus. and I have there suggested 

 that these rings occupy exactly the positions occupied by the interca- 

 lated cartilages of related fishes. The fusion of these cartilages 

 with one another to form a ring, and their further fusion with the 

 bases of the neighboring arches, is a process which might take place 

 secondarily. If this supposition is allowable in the case of Lepisosteus, 

 less objection can be urged in the case of the Urodeles; since 

 here the cartilages in question at no time coalesce with the bases of 

 the arches. We might easily explain the case by supposing that the 

 four intercalated cartilages belonging to each segment have fused 

 and formed a ring ; that this has remained, at least for a long time, 

 in a state of cartilage ; and that the vertebral bands of bone in front 

 ..and behind it have expanded over it and enclosed it between them. 



