342 



ZOOLOGY 



SECT. 



In accordance with their purely aerial mode of respiration, the 

 visceral arches are much more reduced in the Reptilia than in the 

 Amphibia in general. The only well-developed post-mandibular 

 arch is the hyoid, and even this may undergo considerable reduction 

 (Ophidia). The branchial arches are greatly reduced or aborted 

 in the adult. 



There is little variation in the structure of the limb-arches 



,T 



FIG. 1004. Skull of Crocodilus porosus, 

 dorsal view, x about \. Col. buttress 

 connecting the post-frontal with the jugal 

 and ectopterygoid ; F. frontal ; Jg. jugal ; 

 MX. maxilla ; N-a. nasal ; P. parietal ; 

 Pm. premaxilla ; Po. f. post-frontal ; 

 Pr. f. pre-frontal ; Q. quadrate ; Qj. 

 quadrato-jugal ; R. characteristic ridge 

 on the pre-frontal bone ; Sg. squamosal ; 

 T. perforation in the premaxilla caused 

 by a pair of lower incisor teeth. (After 

 Gadow.) 



C&ce 



FIG. 1005. Ventral view of the skull 

 of young Crocodile. Ch, posterior 

 nares ; Coco, occipital condyle ; Jg. 

 jugal ; M. maxilla (palatine pro- 

 cess) ; Ob. basi-occipital ; Orb. 

 orbit ; PL palatine ; Pmx. pre- 

 maxillae ; Pt. pterygoid ; Qj. quad- 

 rato-jugal ; Qu. quadrate. (From 

 Wiedersheim's Comparative Ana- 

 tomy.) 



and skeleton of the limbs in the different groups of Lacertilia. 

 The pelvic arch is distinguished in the Lacertilia in general by 

 its slender character ; and the pubes and ischia are, as in 

 fact is the case throughout the class, separated from one 

 another by wide ischio-pubic foramina a feature which markedly 

 distinguishes the reptilian pelvis from that of the Amphibia. In 

 limbless forms the pectoral arch may be present or may be absent. 

 In the Ophidia all trace of limbs is, as a rule, absent ; but in some 



