liqament socket 



al arch 



suture in young 

 ntercentrum 



parapophysis on 

 intercentrum 



B 



neural arch 



intercentrum 



haemal arch 



Figure 6-13 A-F variation of vertebrae v/ithin the column of Seymouna and the separation of component parts. A, atlas, axis, and 

 3rd cervical- B two dorsals; C, anterior view of a dorsal; D-F, 2nd, 8th, and 23rd caudals. G, component parts of vertebrae as seen 

 in the caudal region of Archegosourus, an eryopsoid amphibian. (A to F after Watson. 1919, and White, 1939; G after Goodnch, 1930) 



neural arch 



ligament canal 

 ligament 



neural canal 



7ft)— spinal cord 



notochord 

 intercentrum 



Figure 6-14. Dorsal vertebrae of the fossil amphibian Eryops in 

 lateral view. A, and as seen from behind, B. (After Williston) 



Figure 6-15. Dorsal vertebrae of Upper Pennsylvanion bronchiosaur, 

 Amphibamus. (After Eaton, 1959, and Gregory, 1950) 



Crvplobranchus and 18 in Necturus; only the first presacral in 

 each lacks a rib. The first vertebra articulates with the skull 

 through 3 facets; its body has a rounded odontoid process 

 which lies between the occipital condyles of the skull and 

 bears a facet on its tip, while what appears to be transverse 



processes bear hollowed facets for the occipital condyles. 

 There is a low neural arch with strong postzygapophyses. 

 The second and succeeding vertebrae, back to the third 

 caudal, bear single-headed ribs. The rib-bearing vertebrae 

 are quite uniform. They have low neural arches, distinct pre- 



152 • THE VERTEBRATE BODY SKELETON 



