VERTEBRAL COLUMN 



13 



ventralia we have to distinguish between the trunk and the tail. 

 In the latter they produce a pair of ventral outgrowths or 

 haemapophyses, which ultimately enclose the caudal blood-vessels. 

 In the trunk 'the basiventral blocks of cartilage are suppressed ; 

 they appear in the early larvae, but disappear during or even 

 before metamorphosis. 



Towards the end of the tail the vertebrae diminish in size, 

 and their constituent cartilages assume a more and more 



Fig. L — 1-5, Five successive stages 

 of the developiDent of a caudal 

 vertebra of a uewt ; 6-7, the 

 second and tlie first cervical ver- 

 tebra of Cnjptohranchus ; 8-9, 

 side view of the constituent 

 cartilaginous blocks of a caudal 

 vertebra (8) and a trunk -ver- 

 tebra (9) of Archegosaurus as 

 typical examples of Temno- 

 spoudylous quadripartite and 

 tripartite vertebrae. The cross- 

 hatched parts indicate the artic- 

 ular facets for the ribs. The 

 anterior end of all the verteltrae 

 looks towards the right side. 

 af. In 7, articulating facet for 

 the occipital condyle ; /J./>,basi- 

 dorsal piece or neural arch ; 

 B.V, basiventral piece or ven- 

 tral arch ; Ch, chorda dorsalis, 

 or notochord ; I.D, interdoisal 

 piece ; I.V, interventral piece : 

 /. V.L, intervertebral ligament ; 

 X, spinal nerve — these are num- 

 bered I, II, III in 6 and 7 ; R, 

 rib ; T, in 7, rib-like tubercle 

 on the first vertebra. 



indifferent shape, until they become confluent into a continuous 

 rod of cartilage, resembling in this respect the Dipnoi and 

 Holocephali. A periodical revival of this rod, at least of its 

 connective tissue, appears in the tail-filament of the male Triton 

 2M(hnatus during the breeding-season. 



The first vertebra, called the atlas, because it carries the 

 head, is remarkable for the possession of an odontoid process-. 

 The latter is formed by a pair of cartilages and represents part 

 of a vertebra, the dorsal portion of which seems to have been 

 added to the occipital part of the cranium. 



