io6 



LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



dermosupraoccipital 

 exocdpital 

 foramen magnum 



quadra tojugal 



tabulare 

 dermosupraoccipital 



nans 

 premaxilla 



premaxilla 



interparietal 

 occipital 



quadratojugal 



D 



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, 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 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 Williston's 

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



