OUR BEST FEATURES 



into a depression or chamber lying considerably 



above the general level of the tooth-bearing 



margins of the upper jaw and they may have 



been the beginning of a fleshy palate. In the 



higher mammal-like reptiles or cynodonts (Fig. 



52 VI) a secondary palate or bony roof of the 



mouth was formed by horizontal ledges that grew 



out from the palatine (pi) and maxillary (mx) 



bones and formed a shelf below the chamber where 



the internal nostrils opened. Very possibly the 



increasing muscular power and mobility of the 



tongue, which pressed against the inner side of the 



upper tooth-bearing bones, may have favored the 



evolution of bony shelves from the palatine and 



maxillary bones. In the mammals (Fig. 52 



VII-X) (including man) this process is carried 



much further so that in the adults the bony palate 



is prolonged much farther backward. To the 



rear end of this bony palate the soft palate was 



attached. In this way the naso-pharyngeal air 



passage was formed, by means of which the 



inspired air is delivered almost directly to the 



windpipe, instead of having to pass through the 



food-containing cavity of the mouth. All this is 



associated in the higher mammal-like reptiles and 



119 



