78 ( X KMPAIIATIVE ANATOMY. 



Charneleontidse, Crocodilia). In most Lizards there is in addition 

 a rod-like bone, the epipterygoid, which extends from the hind part 

 of the pterygoid to the parietals. 



A number of bones arise in connection with the lower jaw, 

 viz. a dentary, angular, supra- angular, splenial, coronoid, and 

 articular (Fig. 62, Dt, Ag, SA, Art). 



In correspondence .with the absence of branchial respiration 

 during development, the branchial apparatus plays no great part in 

 Reptiles, and often only the slightest traces of it are seen : thus 

 in Snakes, for instance, only the hyoid remains, and this not 

 always. In Chelonians a basal piece (basi-hyo-branchial) as well 

 as the first branchial arch persist in addition. 



D. Birds. 



The skull of Birds is formed on the same plan as that of 

 Reptiles, and more particularly of Lizards, although it exhibits a 

 greater proportional development of the brain-case (Fig. 65). The 

 skull of Archa30pteryx was essentially similar to that of existing 

 Birds, and the bones were firmly united together. Teeth were, 

 however, present in both upper and lower jaws, and the fact that 

 the premaxillaB were toothed probably indicates that no horny beak 

 was present (compare the chapter on teeth). 



All the bones have a tendency to run together by the obliter- 

 ation of the sutures originally present between them, and they thus 

 give rise to a united mass largely formed of endochondral bones. 

 It is only in the region of the nose that the cartilage persists 

 throughout life to any extent, and even here not always. In contrast 

 to all the Vertebrata as yet considered, the unpaired occipital condyle 

 no longer lies at the posterior boundary of the skull, but becomes 

 moved downwards and forwards along the base of the skull, so that 

 the axis of the latter lies at an angle with that of the vertebral 

 column. The basis cranii is formed by a basioccipital and a 

 basisphenoid, from which latter a bony rostrum, the remains of 

 the anterior part of the parasphenoid, extends forwards. The 

 posterior part of the parasphenoid persists as a large plate, the 

 basitemporal, which underlies the basisphenoid and part of 

 the basioccipital. Above the rostrum a small presphenoid is present 

 in the embryo. 



All the bones are delicate and spongy, and thus contrast greatly 

 with those of Reptiles, in which they are often of an ivory-like 

 structure. (With regard to the pneumaticity of the bones, 

 already referred to in Crocodiles and certain fossil Reptiles, consult 



wide gape. In most Snakes, and particularly in the Viperine forms (cp. Fig. 176, A), 

 the facial bones are capable of movement upon one another, but in Typhlops they are 

 immovably connected with the skull. The two rami of the mandible are connected 

 by a more or less elastic ligament. 



