ANATOMY OF VERTEBRATES. 



157 



Lizards, ib. D, the palatine 20, and pterygoid 24, form the median 

 boundary, the maxillary, 21, and ectopterygoid the outer one of y. 

 In the Crocodiles, ib. C, the palatine 20 forms the median, the 

 ectopterygoid 25 the outer, the maxillary 21 the fore, and the ptery- 

 goid 24 with the ectopterygoid the hind, boundary. In the Che- 

 Ionia there is no ectopterygoid to divide the pterygo-maxillary 

 vacuity from the lower opening of the temporal fossa. The next 

 openings in point of constancy are the palatal, or posterior, 

 or internal nostrils — ' palatonares ; ' but they are variously formed 

 and situated. In the Menopome, fig. 73, there is no palatine bone 

 to divide them from the pterygo-maxillary vacuity ; in fig. 98 a, 

 the Frog, the transverse palatine forms the posterior boundary 

 of the palatonares, n, the vomer the inner, and the maxillary the 

 outer, boundary; they are similarly encompassed in the Lizards, 



9S 



Frog. 



B 



Tortoise. Crocodile. 



Palatal apertures, Beptilia. 



Iguana. 



ib. d, n. In the Crocodiles, the palatonares, ib. C, n, form a single 

 aperture surrounded by the pterygoids, and situated far back. 

 There is also a single premaxillary foramen, ib. C, p, at the fore 

 part of the bony palate. This is sometimes divided into two by the 

 premaxillary, like the external nostrils, as in the Iguana, ib. D, p. 

 In most Lizards there is a more or less elongate ' interpterygoid' 

 vacuity, ib. d, s, bounded behind by the hypapophyses of the 

 basisphenoid, laterally by the pterygoids, and usually extending 

 some way between the palatines. In the Mosasaurus the inter- 

 pterygoid fissure does not extend far back between the pterygoids, 

 but is bounded in a greater proportion by the palatines. Some- 

 times there is a distinct small ' interpalatine ' vacuity, ib. m, in 



