SKULL. 



407 



thotics remain separate, as does the prootic wliicli forms part of 

 the side wall of the cranial cavity. All the parts of the maxillo- 

 palatine apparatus as well as the quadrate are firmly connected 

 with the bones of the skull. The naso-ethmoidal cartilage 

 largely persists, and is covered dorsally by two bones, which 

 assist in forming the anterior margin of the orbit and occupy the 

 position of the nasal, prefrontal and lacrymal (Fig. 227, 20). 

 The palatines usually have palatal plates which join with a ven- 

 tral expansion of the median vomer to form a hard palate. 

 The premaxillae are small. The maxillae are large and are 



V\is2 





Fig. 228. — Lougitudinal vertical section through the cranium of Chelone midas (from Eey- 

 nolds). 1 parietal, 2 squamosa!, 3 quadrate, 4 basisphenoid, .5 basioccipital, H quadrato- 

 jugal, 7 prootic, <S opisthotic, 9 jsterygoid, lo palatine. 11 rod passed through the narial 

 passage ; 13 exoccipital, IS epiotic. 14 supraoccipital, 15 premaxilla, 16 maxilla, 17 jugal, 

 IS postfrontal, Ut vomer, 2i) prefrontal, 21 frontal. V-XII foramina for exits of the corres- 

 ponding cranial nerves. 



followed by the jugals and quadrato-jugals which reach back 

 to the quadi-ate. The quadrate (Fig. 227, 3) projects down- 

 wards from the periotic and has an articular surface for the 

 mandible. It is overlaid by the squamosal {2). In many Chelo- 

 nia, particularly the marine forms, the temporal fossa is roofed 

 over by bone consisting of a horizontal shelf from the parietals 

 which meets the postfrontals and squamosals (Fig. 227 A). The 

 orbit is completely enclosed by bone, consisting of postfrontal, 

 frontal, prefrontal, maxilla, and jugal. In Cistudo and Geo- 

 emyda the quadrato- jugal is absent and the infra- temporal arcade 



