VERTEBRAL COLUMN 



55 



the Stegocephali of the Carboniferous period, as well as the 

 Perennibranchiata, Derotremata, and many Myctodera, possess 

 simple biconcave bony centra without differentiation of definite 

 articulations. 1 



Thus the bony parts of the vertebrae of Urodeles are not 

 formed from the cartilage surrounding the notochord, but in 



1) 



FIG. 44. LONGITUDINAL SECTION THROUGH THE VERTEBRAL CENTRA of VARIOUS 

 URODELES. A, Ranodon xibericm ; B, Amblystoma tigrinum; C, Gyrinophilu* 

 porphi/rifi'-ii.* (I, 77, ///, the three anterior vertebrae); D, ScUamandrina 



perxpiciUata. 



Ch, notochord ; CK, intravertebral cartilage and fat-cells ; Gp, concave posterior 

 face, and Gk, convex anterior face of centrum with articular socket and head ; 

 Jt-kj invertebral cartilage ; K, superficial bone of centrum ; Ligt, intervertebral 

 ligament ; Mh, marrow cavity ; 7?, transverse process ; S, intravertebral 

 constriction of notochord in Amblystoma, without cartilage and fat-cells ; 

 **, intervertebral cartilage. 



connective tissue, there being only an intervertebral cartilaginous 

 zone, extending into the ends of the centra. In the Anura, on the 



1 In certain of the Stegocephali incomplete hoops of bone, the iiitercentra, 

 and phuroct-Htra, twice as numerous as the arches, surrounded the persistent 

 notochord (cf. the caudal region in Amia and Elasmobranchs, p. 50). 



