Ts'o. 2304. REPTILIAN CHARACTERS IN MAMMALS— WORTMAN. 



45 



As we know so little about the immediate and direct reptilian or 

 batrachian ancestors of the mammals, it is impossible to say just 

 what tlie more precise relations of the quadrate really were originally, 

 but in a general way they could not have been very different in 

 arrangement and disposition to that seen in Splienodon. That the 

 quadrate was well fixed to tlie skull and afforded firm support 

 to the lovv'er jaw is a foregone conclusion, since without such an 

 arrangement the powers of prehension and comminution on tlie part 

 of the teetli could not have developed. If therefore we are to start 

 with a more or less fixed quadrate, braced in a manner not dissimilar 



x^H . 



Psi^O, 



P/n. 



Fig. 15.— Sphenopon punctatus. 0., occipitai.. (Other LETTrBS as in figs. 14 and 16.) 



to that already described inSvlienodon, what would happen to these 

 braces of the quadrate did the brain case commence to enlarge? 

 Obviously the main brace running forwards and inwards to the ptery- 

 goid would be one of tlie first to be encroached upon and inter- 

 fered with, for the reason that it lies almost in contact with the 

 brain case. If the brain enlarged in all directions, which we have 

 every reason to believe that it did, and allowing that th;e pterygoid 

 and temporal muscles remained the same, the space Wjiich they 

 originally occupied would be diminished, and they would in turn 

 exercise pressure upon their enclosing arches and cause profound 

 changes in them. This process would powerfully affect tlie other 

 supports of the quadrate. That somie such factors v/ere operative, 

 and in a large measure responsible for the changes in the quad- 



