224 A MANUAL OF DENTAL ANATOMY. 



Thus, in Myliobates, the powerful jaws are straight from side 

 to side, while their working surfaces from back to front are 

 segments of a circle. The teeth form a thick and strong 

 pavement over the jaws, in the manner of their formation 

 and renewal conforming with the teeth of other Plagiostomi ; 

 the severe use to which they are put being indicated by the 

 extent to which the grinding surfaces of those teeth which 

 have come into use are worn down. 



Several genera have the jaws thus covered, the number 

 of the teeth differing ; thus Myliobates has a central series 

 of very broad, oblong teeth, to the outer sides of which are 

 three rows of small hexagonal teeth ; in (Etobatis the large 

 oblong central plates constitute the whole armature of the 

 jaw. 



The structure of the teeth of Myliobates has already been 

 described and figured (see page 82). 



The Teleostei, or osseous fish, form, the group which com- 

 prises all the fish most familiarly known to us, and within 

 its limits the variation in dentitions is so great that few, if 

 any, general statements can be made about them. It is not 

 uncommon to find teeth crowded upon every one of the 

 bones which form a part of the bony framework of the 

 mouth and pharynx, and the teeth are sometimes in count 

 less numbers. And so great is the variability that even 

 within the limits of single families differences in the teeth 

 are to be found. 



In the common pike the mouth is crowded with sharply- 

 pointed teeth, having a general inclination backwards, and 

 being in some parts of the mouth of larger size than in 

 others. The margin of the lower jaw is armed with teeth of 

 formidable size and sharpness, the smallest teeth being at 

 the front, where they are arranged in several rows, and the 

 largest being about the middle of the side of the jaw. A 

 pike, as is well known to anglers, when it has seized a fish 

 often holds it across its mouth, piercing and retaining it by 



