40 



COMPARATIVE AN ATOM Y. 



periphery occurs in these cartilaginous parts : in the interior of 

 each an articular cavity is formed, so that in the vertebrae of the 

 higher Urodeles (Salamandrina perspicillata and certain Tritons) 

 an anterior convexity aud a posterior concavity may be distin- 

 guished, both covered with cartilage ; they are, therefore, 

 opisthoccelous. A glance at Fig. 31, A to D, will make this clear. 



Liqt 



P> 



FIG. 31. LONGITUDINAL SECTION THROUGH THE VERTEBRAL COLUMN OF VARIOUS 

 URODELES. A, Eanodon sibericus ; B, Amblystoma, tigrinum ; C, Gyrinophilus 

 porphyriticus (the tliree most anterior vertebrae, I, II, III) ; D, Salamandrina 

 perspicillata. 



Ch, notochord ; JvJc, intervertebral cartilage : CK, vertebral cartilage and fat-cells ; 

 K, peripheral bony covering of centrum ; R, ribs and transverse processes ; S, 

 vertebral constriction of notochord in Amblystoma tigrinum, without cartilage 

 and fat-cells ; **, intervertebral cartilaginous tracts ; Alh, Mh, marrow cavities ; 

 Gp, Gk, articular socket and head ; Ligt, intervertebral ligaments. 



In the development of the vertebral column then of Urodeles 

 we can distinguish three stages : (1) A connection of the indi- 

 vidual vertebrae by means of the intervertebrally expanded 

 notochord ; (2) a connection by means of intervertebral masses of 

 cartilage; and finally (3) an articular connection. These three 



