THE SKELETON OF THE NEWT. VERTEBRAE. 139 



large ribs, and a posterior series of caudal vertebrae, all of 

 which except the first few are ribless. 



THE TRUNK VERTEBRAE. 



Any vertebra from the second to the sixteenth may be 

 taken as a type of the trunk vertebrae. 



The general form is elongated and somewhat hour-glass 

 shaped, and the centra are convex in front and concave 

 behind ; an opisthocoelous condition such as this is quite ex- 

 ceptional in Anura. The note-chord may persist interverte- 

 brally 1 , but in the centre of each vertebra it becomes greatly 

 constricted or altogether obliterated, and replaced by marrow. 

 The superficial portion of the centrum is ossified, while the 

 articular surfaces are cartilaginous. The neural arches are 

 low and articulate together by means of zygapophyses borne 

 on short diverging processes. The anterior zygapophyses look 

 upwards, the posterior downwards. Each neural arch is drawn 

 out dorsally into a very slight cartilaginous neural spine. 



On each centrum, at a little behind the middle line, there 

 arise a pair of short backwardly-directed transverse pro- 

 cesses; each of which becomes divided into two slightly 

 divergent portions, a dorsal portion which meets the tubercular 

 process of the rib and is derived from the neural arch, and a 

 ventral portion which meets the capitular process of the rib 

 and is derived from the ventral or haemal arch. The division 

 between these two parts of the transverse processes can be 

 traced back as far as the sacrum. 



The first vertebra as already mentioned differs much 

 from all the others. It has no ribs, and presents anteriorly 

 two slightly divergent concave surfaces which articulate with 

 the occipital condyles of the skull. Between these surfaces 

 the dorsal portion of the anterior face of the centrum is 

 drawn out into a prominent odontoid process, the occur- 

 rence of which renders it probable that the first vertebra of 



1 i.e. between one vertebra and the next. 



