THE SKELETON OF REPTILES 



21 



closely to their special uses, either by increase in size, or by modifi- 

 cations of their shape and structure. 



SKULL AND TEETH 



The skull of reptiles is much more primitive or generalized in 

 structure than is that of mammals, to such an extent, indeed, that 

 there is yet much doubt as to the precise homologies of some of the 

 bones composing it; and, inasmuch as the names were originally 

 given, for the most part, to the bones of the human skull, there is 

 still some confusion among students as to the proper names in 



all cases, a confusion that doubt- 

 less will not be wholly dissipated 

 until we know much more about 

 the early or more primitive 

 reptiles than we do at present. 



Fig. 4 Fig. 5 



Fig. 4. — Seymouria, a primitive cotylosaurian. Skull, from above: pm, pre- 

 maxilla; n, nasal; /, lacrimal; p, prefrontal; /, frontal; pf, postfrontal; it, inter- 

 temporal; st, supratemporal; sq, squamosal; ds, dermosupraoccipital ; /, tabulare; 

 j, jugal; po, postorbital; m, maxilla; s, surangular; ang, angular; pa, parietal. 



Fig. 5. — Seymouria, skull from the side. Explanations as in fig. 4. 



As in other parts of the skeleton, there has been a reduction 

 in the number of parts of the reptile skull from that of the more 

 primitive forms, and a better adaptation of those which remain 

 for the special uses they subserve. This reduction in number has 

 been caused in part by the actual loss of bones, in part by the fusion 

 of contiguous ones. The most primitive reptiles had no less than 

 seventy-two separate bones in the skull; 1 the human skull has 



1 Paired maxillae, premaxillae, nasals, prefrontals, lacrimals, frontals, parietals. 

 dermosupraoccipitals, tabularia, supratemporals, intertemporals, squamosals, jugals, 

 quadratojugals, postorbitals, postfrontals, quadrates, exoccipitals, paroccipitals, 

 vomers, palatines, pterygoids, sphenomaxillae, stapes, transverse, alisphenoids or 

 orbitosphenoids, epipterygoids, articulars, prearticulars, angulars, surangulars, coro- 

 noids, splenials, dentaries, one supraoccipital, one basioccipital, one basisphenoid, 

 one ethmoid. 



