frontal 



squamosal 



mesethmoid 

 nasal 



prefrontal 



subarcuate fossa 



supraoccipitol 



epiotic 



endolymphatic 

 foramen 



dentary 



exoccipitol 

 opisthotic 

 prootic 



basioccipital 

 basisphenoid Xjugular foramen 

 articular 



s'plenial 1 t ^angular 



supraangulor 1 



^ preorticular 



egg tooth 

 premoxilla 



dentary / preort 

 splenia 



Figure 4-14. Head skeleton of the chick. A, medial view of right half of skull and mandible; 

 B, ossifications of embryo of 1 1 -days incubation; C, hyoid apparatus as viewed from below. 



from reptile. There is some divergence of thought as to 

 whether the position of this line should be based on mor- 

 phology or function. 



A review of the origin of the reptiles, and the therapsid 

 line which gave rise to the mammals, should follow a con- 

 sideration of the diversity and evolution of the Amphibia. 



Living amphibians 



The ancestral amphibian is assumed to have evolved from 

 some fish-like form; therefore, it must have been quite dif- 

 ferent from the living representatives, which lack gills and 

 have limbs rather than fins. 



78 • HEAD SKELETON OF OTHER TETRAPODS AND CHOANATES 



