298 



THE AMERICAN NATURALIST 



[Vol. XL 



Individual teeth are frequently broken off, but whether they are 

 ever regenerated again the writer is not able to say. 



The coronoid (Co.) is a spindle-shaped bone that lies on the 

 inner side of the mandible near its posterior end. Its inner or 

 medial surface is smooth and rounded except near the middle of 

 its length, where it is elevated and roughened to form the coronoid 

 process for tlie attachment of muscles. In the anterior corner of 

 the triangular depression between the dorsal borders of the dentary 

 and coronoid bones is a small canal leading towards the anterior 

 end of the jaw. It may be c^alled the alveolar canal. A ventral 

 view of the jaw shows a more evident canal (Ct.) entering between 

 the dentary and coronoid bones, just at the anterior end of the 

 angular, as seen from the surface but really at some distance 

 behind this end as the anterior portion of the angular is hidden 

 between the two other l)ones. This canal corresponds, perhaps, 

 to the inferior dental foramen of higher forms. The canal that 

 Osawa describes, in this region, passes directly through the coro- 

 noid bone; he calls it the "canalis chords tympani." The outer 

 surface of the coronoid (hidden, of course, by the other bones) 

 is deeply grooved longitudinally to receive a long, slender proc- 

 ess of the angular (Fig. 4). 



The angular (A.) forms the posterior end of the mandible and 

 presents there an articular surface for attachment to the quadrate. 

 This articular surface is triangular in outline, with the apex of the 

 triangle towards the {)()steri()r. The articular portion of the angu- 

 lar is a thick mass of cartila-v. :ni<l cxtnuLs forward to fill the 

 angular space between the dentary and coronoid bones that has 

 ah-eady been mentioned. Anterior to this angular space, this 

 cartilage is continued forward as a long, slender rod (Meckel's 

 cartihige) lying in a furrow between the dentary and the coronoid. 

 Meckel's cartilage e\tend> for nearly three fourths of the length 

 of the jaw, or to about the nnd.He of the row of teeth. The part 

 of the aii-uhir that seen from the ventral aspect (Fig. 1, A) is 



(h.tance, anteriorly, between the dentary and thtXoronoid. In 

 fact it exteiKis farther in an anterior direction tluui i. seen from 

 the surface, being covered for some distance by the conjnoid. 

 The hyoid apparatus (Fig. 5), using that term to include both 



