SKULL OF VERTEBRATA. 



461 



Saurii, Aves), articulations, more or less well developed, appear in 

 those parts of the maxillo-palatine apparatus which are attached to it. 

 These are not present in the Crocodilini and Ohelonii, where the 

 quadrate is jammed between the squamosal and the bones of the 

 auditory capsule. Sphenodon presents an intermediate arrangement; 

 its skull is on the Saurian type, but the quadrate is firmly united 

 with the pterygoid and squamosal. 



B 



§ 349. 



Two sets of bones, which extend f orwards, are attached to the quad- 

 rate, just as in the Amphibia. Nearer the middle line we find — in 

 Birds, Serpents, and Lizards 

 — the pterygoid (Fig. 250, 

 Pt) articulated with the base 

 of the cranium. The two 

 bones are united suturally 

 in the middle line in the 

 Ohelonii and Crocodilini, and 

 are also firmly attached to 

 the base of the skull (Fig. 

 251, Pt) ; in the latter they 

 bound the posterior nares. 

 In the Ophidii, Saurii, and 

 Crocodilini, there is an ex- 

 ternal pterygoid (Os trans- 

 versum, Figs. 250, A Tr; 

 251, B Tr) which connects 

 the pterygoid with the 

 maxilla; it is uncertain 

 whether this corresponds to 

 the ectopterygoid of fishes. 



In front of the ptery- 

 goid lie the palatines (Pal) ; 

 in the Chelonii and Croco- 

 dilini they are united su- 

 turally in the middle line, 

 but in the Ophidii, Saurii, 

 and Aves, they are separated 

 from one another and form 

 the lateral boundaries of 

 the posterior nares (Fig. 

 250, Pal). In the Chelonian 

 skull the vomer (Fig. 251, A Vo) reaches to the roof of the cavity 

 of tbe mouth and lies between the palatines, while above the nasal 

 cavity the palatines unite together at the base of the cranium. In 

 Birds the palatines are generally long and flat bones (Fig. 250, B 

 Pal), which are connected at their anterior end with a process of 

 the maxilla (Mx) } or fused with a process of the premaxilla. 



C 



Fig. 250. View of the base of the skull. A Of 

 Monitor. B Of Struthio. Ob Basi-occipital. 

 C Occipital condyle. Ol Exoccipital. Spb Basi- 

 sphenoid. Q Quadrate. Pt Pterygoid. Tr Trans, 

 verse. Pal Palatine. V Vomer. Qj Quadrato- 

 jugal. Ju Jugal. Mx Maxilla. Mb' Its median 

 process. Px Premaxilla. 



