postorbital 



parietal 



suprooccipital 



uamosal 



dentary- 

 calcified Meckel's cartilage 



angular 



pterygoid 

 postorbital 

 basisphenoid 

 basioccipital 



quodratojugal ^^-^^y^^^-^^ 



quadrate squamosal 



frontal 



prefrontal, 

 prootic 



uodrate 

 opisthotic 

 lasioccipital 

 basisphenoid 

 quadrate 

 rticulor 

 prearticular 



suprooccipital 

 parietal 



postorbital 

 maxilla 



opisthotic 

 uamosal 



columella 



exoccipital _ 



carotid cono 



pterygoid 



.quadrate 



basisphenoid 

 basioccipital 



foramina 



Figure 4-9 Skull and mondible of the Turtle based on Lepidachelys and Carettc. A, lateral view 

 of skull and mond.ble; B, dorsal view of skull; C, ventral view of skull; D, medial view of right half 

 of skull and mandible; E, rear view of skull. 



root as in the mammal. The skull is nonkinetic. It is pecul- 

 iar in being pneumatic; that is, tfiere are sac-like outgrowths 

 from the middle-ear cavity wfiich lie between or within the 

 surrounding bones. 



The lower jaw (Figure 4-11 D,E) lacks a prearticular, 

 which is largely replaced by the angular. A small preartic- 

 ular fragment is said to appear in the embryo but later fuses 



with the articular. The hyoid apparatus consists of a broad 

 plate, the copula, to which is attached the first cerato- 



branchial. 



In its development, the head skeleton of the crocodilian 

 (Figure 4-12) is quite different from that of the lizard or the 

 turtle. Some of the special features will be mentioned in com- 

 parisons with the bird. 



72 



HEAD SKELETON OF OTHER TETRAPODS AND CHOANATES 



