304 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 8J 



ectostylid is only slightly developed in the premolars except in early 

 wear and in the molars is generally feeble or absent. 



With advanced wear (fig. 22, no. 12504 and no. 12546) the walls 

 of the outer columns become more convex, and the lingual reentrants 

 are reduced in extent and are more compressed. The hngual walls 

 of the inner columns are well rounded except for the metastylid, 

 which may become more acute posteriori}^. The anterior lingual fold 

 shows the most marked reduction with the outer median fold most 

 persistent. The anterior branch of the posterior hngual fold is also 

 retained relatively late. 



The differences between m.olars and premolars of the lower denti- 

 tion are very noticeable, and in addition to the greater size of the 

 premolars the two principal enamel loops from the inner wall are 

 more deeply impressed and less transversely compressed than in the 

 molars. In the posterior reentrant the anterior wing extends almost 

 to the anterior loop and hngually nearly to the groove between the 

 metaconid and metastylid, noticeably constricting the union be- 

 tween these columns. In the molars the reentrant from the outer 

 surface between the protoconid and hypoconid extends nearly to 

 the groove between the metaconid and metastylid, widely separat- 

 ing the contiguous portions of the anterior and posterior hngual 

 folds. The hypoconulid is more shortened anteroposteriorly in the 

 premolars. In the molars this cusp reaches its maximum develop- 

 ment in Ms and is moderately well developed in slightly worn Mi 

 and Ma. 



Inferior deciduous dentition. — As is true of the young skulls, a 

 relatively large number of the immature mandibles are in a stage of 

 development in which the milk premolars are in moderately early 

 wear with Mi just erupting, probably a httle less than a year old, 

 meeting death perhaps early in spring. The replacement of the 

 lower milk teeth is in the same order as in the upper jaw, Dii is 

 first to go, followed by the milk premolars in order, and Di2 as M3 

 erupts. Dis is replaced about the time P4 and M3 commence wear. 



The lower milk incisors are simple, low crowned, and shallow 

 cupped. The cup in Dis is usually imperfectly formed or nearly 

 absent, and in a few specimens there is a small cusp or a style in 

 the middle or anterior portion of the embayment. In no specimen 

 was a milk canine observed. A small opening at about the position 

 of the canine might well be a foramen such as is seen in recent 

 immature mandibles. 



The well-cemented lower deciduous premolars (fig. 22, no. 12560 

 and no. 12785) though hypsodont are relatively short crowned 

 compared to the permanent cheek teeth. The milk teeth are narrow 

 and relatively elongate anteroposteriorly. The columns are trans- 

 versely compressed and generaUy show simple or little-phcated 



