306 



F. B. Loomis — Osteology and Affinities 



but 9 ,nm deep. However, the tooth is available for much 

 greater wear than the depth of the pit ; for as age in creases 

 the pulp cavity fills with dentine and makes some 18 mm more 

 available. The great height of these teeth is the cause of the 

 great depth of the lower jaw noticed in the description of the 

 mandible. 



Milk dentition. — Young jaws are found in surprisingly 

 large numbers, practically all of them being of about the same 

 age, and showing the full milk dentition, together with the 

 unworn first molar. These skulls are entirely disarticulated, 

 and I have seen no incisor or canines of the upper jaw, though 

 they were doubtless there. The first upper premolar is situ- 

 ated near the canine and behind it is a considerable diastema, 

 between it and the second small pointed premolar. It is on 



Fig. 



Fig. 8. 



Fig. 7. Stenomylus hitchcocki, section of third lower molar to show 

 depth of pit. x 1/1. 

 Fig. 8. Upper premolars of the milk, dentition, x 1/2. 



the third and fourth of this series that the burden of grinding 

 is thrown. Like adult molars, they are strongly hypsodont 

 with high crescentric crests and deep pits. They differ, how- 

 ever, in having the outer face more convex over the paracone 

 and metacone, and in having a well-developed mesostyle as 

 well as a parastyle; from which it may be concluded that 

 these features were also present on the teeth of the ancestral 



Fig. 9. 



Fig. 9. Stenomylus hitchcocki, mandible with the milk dentition, x 1/2. 



form. The third and fourth deciduous premolars are each 

 two-lobed and< in general resemble the permanent molars. 



Lower jaws are usually the better preserved, the alveoli for 

 the three incisors and the canine being present on several 

 specimens. The canine is grouped with the incisors as in the 

 adult. The first premolar is represented by a tiny alveolus 



