THE CHELONIAN SKULL. 



•205 



internasal plate, whicli expands below, and joins the pala- 

 tine plate of the palatine bone. 



Above the posterior and upper part of the orbit lies a 

 postfrontal, and, behind this, a squamosal is placed at the 

 sides of the periotic capsule, and above the large quadrate 

 bime. The postfrontal and squamosal occupy the upper 

 part of the temporal region of 

 the skull. Below these, a quad- 

 rato-jugal and a jugal connect 

 the quadrate bone with the large 



maxilla. 



In some genera, as Clielone and 



Chehjclra, the skull possesses a 



sort of false roof, formed by the 



expansion of a median ridge, de- 

 veloped from the parietal bones, 



into a broad plate, which becomes 



suturally united with the post- 



frontals and squamosals. 



The quadrate bone is firmly 



fixed to the sides of the pei-iotic 



region of the skull, and ends 



below in a strong condyle for 



the mandibles. The long and 



broad pterygoid bones unite with 



one another in the middle line. 



and are firmly fixed to the base 



of the skull, as in Plesiosauria 



and Crocodilia. They unite 



only with the upper part of the 



quadrate bone, a.s in the latter 



reptiles. 



The palatines are firmly united with the pterygoids. 



behind, and with the vomer above and in front. They 



are prolonged downwards, and develope a short palatine 

 plate, which imites with the produced and expanded lower 



edge of the vomer, to bound the posterior nares. (Fig. 67, 

 Vo,N\) 



Fig. 67.— The left half of tlie 

 underside of the skull of a 

 Turtle: iV', posterior nares. 



