694 COMPARATIVE ANATOMY 



The occipital is divided into: 



A supraoccipital, an exoccipital on each side, and a basioccipital. 

 These four bones form the borders of the foramen magnum. 



dermosupraoccipital 



e*occipital 

 foramen magnum 



rental 

 frontal 



orbit 

 jugaJ 



postfrontal 

 postorbita! 

 intertemporal 

 squamosal 

 supratemporal 

 parietal 



quadratojugal 



tabulare 

 dermosupraoccipital 



nans 

 aremaxilla 



prefrontal 



lacrimal 



frontal 

 jugal 



orbit 

 lateral temporal 



arcade 



postprbital bar 

 postfrontal 

 parietal 

 lateral temporal 



fossa 



squamosal 

 quadrate 



supratemporal 

 arcade 



interparietal 

 occipital 



quadratojugal 



Fig. 413. 



Dorsal view of the skulls of four representative vertebrates to show changes 

 and reduction of the membrane bones of the roof. A, skull of an extinct amphibian, 

 Capitosaurus, belonging to the Stegocephala; note the large number of membrane 

 bones completely roofing the skull. B, skull of one of the most ancient reptiles, 

 Seymouria, belonging to the Cotylosauria ; the membrane bones are nearly as 

 numerous as in the amphibian, are similarly arranged, and completely roof the 

 skull. C, skull of a modern reptile, the alligator ; several of the membrane bones 

 which were present in the extinct forms have been lost, and the roof has several 

 openings. D, skull of a modern mammal, the dog, showing still greater loss of 

 membrane bones. Membrane bones blank; cartilage bones stippled. (From 

 Hyman's "A Laboratory Manual for Comparative Vertebrate Anatomy," A, after 

 Reynolds, B, after Williston, by permission of the Chicago University Press.) 



