XIII 



PPIYH'M CHORDATA 



U:i 



tlie exception of the Crocodiles. Sometimes this occurs iii a 

 fragmentary manner ; but in Snakes and many Lizartls the whole 

 comes away as a continuous slough. 



Endoskeleton. — The vertebno arc always fully ossified. Only 

 in the Geckos iwul Sphcuodon (Fig. 981) are the centra ain[)hi(xjulijus 

 with remnants of the notochord in the inter- 

 central spaces In most of the others the 

 centra are procoelous, a ball-like convexity on 

 the posterior surface of each centrum projecting 

 into a cup-like concavity on the anterior face 

 of the next. In Sphenodon and the Geckos a 

 series of wedge-shaped discs {mtercentra) are 

 intercalated between the vertebra? of the cer- 

 vical, part of the thoracic, and the caudal regions. 

 The paired bones of the inferior arches {chevron 

 hones) are attached to these bones when they 

 are present. In the Lizards in general and the 

 Crocodiles, there are inferior processes (Jiyi)(q)o- 

 physes), perhaps representing intercentra, situated 

 below the centra of the anterior cervical vertebra- 

 Sphenodon, and the Crocodiles there is a median bone, the pro- 

 atk(-s (Fig. 985, 0), intercalated between the atlas and the occipital 

 reoion of the skull. 



In the Snakes and in Iguanas, in addition to the ordinary 

 articulating processes or zygapophyses, there are peculiar articular 

 surfaces termed zygosphenes and zyyantra (Fig. 982). The zygosphene 



Fii:. 'jsi.— \'i:rtcbra of 

 Sphenodon, shuw- 



iiig' tlic ;impliic<olous 

 cciitruiii (C. ). (After 

 Hoadley.) 



In Chameleons, 



Fig. 9S2. — Vertebra of Python, anterior and posterior views. /!. .■>■. neural spine ; p. z. pre- 

 zygapophyses ; pt. ;. post-zygapophysis ; /. p. transverse processe.s ; .:. a. zygantruin ; z,s. zygo- 

 sijhene. (After Huxley.) 



is a wedge-like process projecting forwards from the anterior face 

 of the neural arch of the vertebra, and fitting, when the vertebrse 

 are in their natural positions, into a depression of corresponding 

 form — the zygantrum — on the posterior face of the neural arch 

 of the vertebra in front. To this arrangement, as well as to the 



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