io6 



LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



premaxilla 



nans 



maxilla 



nasal 



lacrimal 



prefrontal 



frontal 



jugal 



orbit 



postfrontal 

 postorbital 

 parietal 

 supratemporal 



squamosal 

 r jadratojugal 

 tabulare 

 quadrate 



dermosupraoccipital 



exoccipital 

 foramen magnum 



prefrontal 



frontal 

 orbit 



jugal 



postfrontal 

 postorbital 

 intertemporal 

 squamosal 

 supratemporal 

 parietal 



quadratojugal 



tabulare 

 dermosupraoccipital 



B 



prefrontal 

 lacrimal 



frontal 

 jugal 



orbit 

 lateral temporal 



arcade 



postorbital bar 

 postfrontal ~ 



parietal 



lateral temporal 

 fossa 



squamosal 

 quadrate 



supratemporal 

 arcade 



supratemporal 

 fossa 



premaxilla 



nans 

 nasal 



frontal 



zygomatic 

 arch 



temporal 



parietal 



interparietal 

 occipital 



quadratojugal 



FIG. 36. Dorsal view of the skulls of four representative vertebrates to show the reduction of the 

 membrane bones of the roof in the course of evolution. A, skull of an extinct amphibian, Capilosaurus , 

 belonging to the Stcgocephala; note the large number of membrane bones completely roofing the skull. 

 B, skull of one of the most ancient reptiles, Scymouria, 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 present in the extinct 

 forms have been lost, and the roof bears several openings. D, skull of a modern mammal, the dog, 

 showing still greater loss of membrane bones. Membrane bones blank; cartilage bones stippled. 

 (.4 from Reynolds' The Vertebrate Skeleton, courtesy of the Macmillan Company; B from Williston's 

 Water Reptiles of the Past and Present, University of Chicago Press.) 



