notochord 



vertebral ring 



MAMMAL 



r 



perichordol tube 



bony centrum 



nucleus pulposus in 



intervertebral body 



fibrous connective tissue 



of intervertebral body 



vertebra! ring 



B 



notochord' 



intervertebral body 



bony centrum 



.fibrous connective tissue 



ossified intervertebral body 

 fused to centrum 



notochord 



FROG 



Figure 6-21. Vertebral as compared with intervertebral constriction of the notochord as observed 

 in the mammal, A, and the frog, B. (After Remane, 1936) 



but in the caudal region it is thicker and the dorsal and ven- 

 tral arch components become joined by a connective tissue 

 band. 



Rhipidistian The vertebral column of Eusthenopteron is well 

 known (Figure 6-25). In this type, the notochord is essentially 

 unconstricted. There is a pair of large intercentra which ex- 

 tend nearly around the notochord, with only a short gap 

 separating the dorsal ends. The neural arch rests on the 

 upper ends of the intercentra. Behind the base of the neural 



arch of either side, is a small interdorsal (or interneural) 

 arch which is notched along its anterodorsal margin for the 

 roots of the spinal nerve. The arrangement of parts is much 

 like that in the ichthyostegid amphibian (Figure 6-16), and 

 the similarity is carried even further in that a short rib 

 articulates along a line beginning low on the intercentrum 

 and ending on the ventral margin of the neural arch. The 

 rib is, however, single-headed. 



The crossopterygians and some of the dipnoans seem to 

 have essentially the same sort of vertebral column. That of 



ossified neural spine 



notochord | \\^ J 



Figure 6-22. Vertebral structure of Neocerafodus. A, lateral view of thoracic (dorsal) vertebrae; 

 B, end view of thoracic; C, lateral view of anterior coudols; D, posterior caudals. (After Remane, 

 1936) 



THE VERTEBRAL COLUMN 



157 



