328 



ZOOLOGY 



SECT. 



a broad process of the pteiygoid against which the inner sur- 

 face of the mandibular ramus plays. 



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, except in so far as 

 they contribute to the formation of the tracheal rings, are not 

 represented in the adult, with the exception of most Chelonia, 



in which the first branchial arch 

 persists. 



There is little variation in the 

 structure of the limb-arches 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 well developed or may be 

 absent. In the Ophidia all trace of 

 limbs is, as a rule, absent ; but in 

 some Pythons vestiges of hind-limbs 

 are to be detected in the form of 

 two or three small bones which sup- 

 port a small horny claw. 



In Hatteria (Fig. 928) there is a 

 foramen above the outer and one 

 above the inner condyle of the 

 humerus. There are eleven carpal 

 elements, of which there are four, 

 including a pisiform, in the proximal 



row, two centrals, and five in the distal row. The pubes are 

 united in a symphysis, in front of which is a cartilaginous epipubis. 

 A large oval obturator foramen intervenes between the ischium 

 and the pubis. In the tarsus the tibial and fibular elements are 

 distinct, though firmly united. The intermedium and the centrale 

 are firmly fixed to the tibiale. There are three distal tarsal bones. 

 In the Chelonia (Fig. 930) the interclavicle (episternum) and 

 clavicles are absent, unless the former be represented by the median 

 element of the plastron. The entire pectoral arch is a tri-radiate 



Coce 



FIG. 937. Ventral view of the skull of 

 young Crocodile. C'h, posterior 

 nares ; Cocc. occipital condyle ; ./>/. 

 jugal ; M. maxilla ; Ob. basi-occipital ; 

 Orb. orbit ; PL palatine ; Pmx. pre- 

 maxillae ; Pt. jpterygoid ; Qu. quad- 

 rate; Q.J. quadrato-jugal. (From 

 NViedersheim.) 



