No. 472] ANATOMY OF CRYPTOBRANCHUS 297 



life. It forms the supporting framework to the floor of the capa- 

 cious mouth and throat so important in the process of inspiration. 



The mandible or lower jaw (Figs. 1, 2, 4) is made up of two- 

 distinct parts, joined together anteriorly, in the middle line, by 

 a short ligament of cartilage, the mandibular symphysis. As 

 may be seen from the figures, the curve of the anterior margin 

 of the mandible is not so wide as that of the upper jaw, so that 

 the two jaws do not fit together very closely. Each half of the 

 mandible is made up of three elements: the dentary, the coro- 

 noid, and the angular. 



The dentary (D.)is the largest of these three bones, and extends, 

 from the symphysis almost to the posterior angle of the jaw. Its 

 anterior end is thick and rounded, while the posterior end is thin 

 and pointed to fit against the outer 

 surface of the angular. The ventro- 

 anterior surface of the dentary is 

 smooth, and is marked by a series 

 of about six small openings, mental 

 foramina, which do not show in 

 either a ventral or a dorsal view of 

 the mandible. The dorso-posterior, 

 or upper-and-i.mcr, border of the 

 <lentarv is .lep.vssrd to form a deep 

 alv.M.hir surface, alonix the outer bor- 

 der of which are situated the small 

 conical teeth in a single row. There 

 are about forty-five teeth in each 

 dentary. The alveolar surface ex- 

 tentls for somewhat more than two 

 thirds of the entire length of the 

 bone, and ends posteriorly at the 

 point where the dentary meets the Fio. 4.— The b.m.s .>f tiie maiuiibie, 

 outer border of the coronoid. The coronoid : /->.. .i. mary. ^ ' ' 



smaller than the rest. They are attached to the bottom and side 

 of the alveolar depression, so that their crowns soinctiiucs project 

 but a short distance above the upper border of the dentary l)oiie. 



