io6 



LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



lacrimal 



prefrontal 



frontal 



jugal 



orbit 



postfrontal 

 postorbital 

 parietal 

 supratemporal 



squamosal 



r'^adratojugal 



tabulare 



quadrate 



dermosupraoccipital 

 exoccipital 



orbit 

 jugal 



postfrontal 

 postorbital 

 intertemporal 

 squamosal 

 supratemporal 

 'parietal 



quadratojugal 



tabulare 

 dermosupraoccipital 



B 



nans 

 premaxilla 



premaxilla 



supratemporal 

 arcade 



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 Stegocephala; note the large number of membrane bones completely roofing the skull. 

 B, skull of one of the most ancient reptiles, Seymour ia, 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. 

 (A from Reynolds' The Vertebrate Skeleton, courtesy of the Macmillan Company; B from Willis ton's 

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



