XTIT 



PHYLUM CHORDATA 



rarnus plays, an arrangement which occurs also in most 

 Lacertilia. 



In accordance with their purely aerial mode of respiration, the 

 rixri'i'al arches are much more reduced in the Reptil.ia 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 laryngeal cartilages, are not 

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

 which the first and second branchial 

 arches persist as cornua of the hyoid. 



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 present 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 support 

 a small horny claw. 



In Sphenodon (Fig. 984) there is 

 a foramen above the outer and one 

 above the inner condyle of the 

 hum ems. There are eleven carpal 

 elements, of which there are four, 

 including a pisiform, in the proxi- 

 mal 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 foramen intervenes between the ischium 

 and the pubis. A cartilaginous Tiypo-iscliium is attached to the 

 ischia behind. 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 Chclonia (Fig. U86) the intcrclavicle (episternum) and 



Coec 



FIG. 994. Ventral view of the skull of 

 young Crocodile. CVt, posterior 

 nares ; C'occ. occipital con iyle ; Jg. 

 jugal ; M. maxilla (palatine process ) ; 

 Ob. basioccipital ; Orb. orbit; PL 

 palatine ; Pmx. premaxillai ; Pt. 

 pterygoid ; Qj. quadrato- jugal ; Qu. 

 quadrate. (From Wiedershcim's Com- 

 parative Anatomy.) 



