OUR FACE FROM FISH TO MAN 



upper jaws, the premaxilla and maxilla, bear 

 compressed conical teeth. The dentary plate of 

 the lower jaw (Fig. 64) covering the outer side of 

 the primary lower jaw or Meckel's cartilage, bears 

 a row of conical teeth which fit between the 

 marginal teeth of the secondary upper jaw and 

 the larger teeth on the dermal plates covering the 

 primary upper jaw. Thus we have the teeth of 

 the secondary upper jaw over-hanging or biting 

 outside of those of the dentary or lower jaw, an 

 arrangement that persists throughout the sub- 

 sequent series upward to the primitive mammals, 

 traces of it even being preserved in man. The 

 coronoid bones, covering the inner side of the 

 primary lower jaw, in the lobe-finned fish bear large 

 teeth which doubtless sheared into the struggling 

 prey and pressed it against the large teeth on the 

 roof of the mouth. Thus neither the Meckel's 

 cartilage, or primary lower jaw, nor the palato- 

 quadrate, or primary upper jaw, now have any 

 direct relations with the teeth, which are supported 

 entirely on their own bony plates, as they are in 

 all higher vertebrates, including man. The pri- 

 mary lower jaw from this point onward takes a 



subordinate part, except that its nearer (proximal) 



110 



