46 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 5T» 



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Ju. 



yuj: 



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Fia, 



rate, is strongh- suggested by the modifications of the legmen 

 temporalis or temporal bony roof of the more primitive Reptilia. 

 Certain fenestrae or vacuities were formed in this bony coverings 

 I apprehend as a result of muscular pressure, in order to allow 

 more space for the expanding muscles when powerfully contracted. 

 As the bram case continued to enlarge it finally reached a point. 



where the squamosal came in contact 

 with it and was applied to its outer wall,, 

 receiving its support and stability from 

 this source and no longer existing as- 

 an expanded and widely separated arch. 

 Since there must at all times have 

 existed the most intimate relations be- 

 tween the movements of the jaw, the 

 dental armature and the temporal and 

 pterygoid muscles, as well as their area, 

 and points of attachment, and as these 

 in turn reacted upon the bony supports 

 of the quadrate, we may safely conclude, 

 it seems to me, that the diminution and 

 final loss of the quadrate may be traced 

 directly to and was the logical result of 

 these interacting mechanical forces and 

 factors. As the quadrate lost its bony 

 supports and braces and was no longer 

 capable of furnishing a proper fulcrum for the leverage of the jaw, 

 the articulation began to shift forward upon the more fixed squamosal 

 where the joint was finally located, the quadrate dwindling away to 

 the inconsiderable vestige which has already been discussed. If 

 therefore, these modifications of the quadrate, the arches, the teeth,, 

 the jaws, and, more than likely, the palate as well, are traceable to 

 these causes which were primarily inaugurated by the enlargement of 

 the brain, or, in other words, those ver}^ changes which transformed 

 the reptile or batrachian into the mammal in so far at least as the 

 skull is concerned, then the interesting question arises were these 

 modifications confined to a single group of reptile-like forms, or is it 

 not possible that they could have been inaugurated in widely sepa- 

 rated groups quite independently? If the progressive enlargement 

 of the brain has been one of the prime determining factors in the 

 process, then it would appear probable that it was not confined to 

 any one group of promammalian reptiles or batrachians any more than 

 this special character is confined to any particular group of mammals 

 today. It is a well-kno^vn and universally recognized fact in evolu- 

 tion that similar habitat, envu-onment, and conditions have produced 

 similar structures to such an extent that it is often difficult to say- 



16.— Sphenodon functatus. B. 

 oc, basioccipital; B. sp., basispue- 

 noid; lat. t. v., lateral temporal 

 vacuity; pi., palatine; Ft., pteev- 

 GOId; Pt. proc. q., pterygoid process 

 OF quadrate; Quad., quadrate; Sta., 

 stapes; Sup. t. v., supra temporal 

 VACUITY. (Other letters AS IN FIG. 14.) 



