328 



AM10IDE1 



dealt with, the vertebral centra, formed in the skeletogenous layer 

 in connection with the bases of the neural and haemal arches, 

 are derived almost equally from the dorsal and the ventral 

 elements ; with the help of bony tissue these are bound together 

 into a single ring-like or biconcave centrum. Now in Amia well- 

 developed bony centra occur along the trunk region, each bearing 



Fio. 306. 

 A, B. C. diagram of three regions of the vertebral column of Euryeormus. (From A. S. 

 Woodward, Vert. Palaeontology.) h. haemal arch ; he, hypocentrum ; >ij neural arch ; pi, pleuro- 

 centrum. D, ieft-side a iew of three segments of the vertebral column of :i . "5 cm. long Amia 

 calm, taken at the .junction between trunk and tail. 1. basidorsals (neural arches) ; 2, inter- 

 dorsals; 3, basiventrals; 4, interventrals. (After Schauinsland, from Hertwig's Hamdbvch.) 



a neural arch surmounted by a spine, and, except in the first two 

 segments, basiventrals which carry the long pleural ribs. The 

 neural arches are separated from the centra by cartilage, and a pair 

 of cartilaginous nodules are found between them (the interdorsals). 

 Farther back, in the caudal region (except at its extremity), there 

 appear to be alternate centra with and without arches. Here occur 

 anterior centra bearing a pair of vestigial cartilaginous interdorsals 

 and a pair of similar interventrals, followed by posterior centra 



