28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



comparatively small but in no specimen are they clearly defined, and 

 the extent of premaxillary exposure in the palatal view would appear 

 to be limited to the rim of bone supporting the incisors anterior to the 

 canines. In the posterior portion of the palate the palatines extend 

 forward to a position about even with the anterior portion or mar- 

 gin of the first molar. The posterior palatine foramina may show one 

 or two openings on each side, on or near the suture between the 

 maxillae and palatines, inward from about the posterior portion of 

 M 1 . Posteriorly this suture comes near or reaches the alveolar mar- 

 gin of the last two molars. The posterior narial aperture is a little 

 more than half the width of the palate between the third molars and 

 extends forward to a position about even with or slightly in advance 

 of the anterior margin of the third molars. The forward margin of 

 the aperture is gently rounded to nearly rectangular in outline and 

 exhibits a slightly everted liplike rim in a forward continuation of the 

 inferior margin of the ascending plates of the palatines bounding the 

 narial aperture. Lateral to this lip or crest and medial to the 

 prominent maxillary tuberosity, the posterior margin of the palatines 

 may show a pronounced though broadly rounded notch. 



The palate in Phenacodus is lower with respect to the basicranium 

 than in Meniscotherium, in keeping with the relatively deeper ros- 

 trum of Phenacodus. It is also noted that the notch between the 

 ascending plate of the palatines and the maxillary tuberosity is more 

 constricted in Phenacodus and extends forward more deeply grooved 

 on the ventral surface of the palate. 



The palate in Hyopsodus is rather like that in Meniscotherium 

 and Phenacodus with the palatines extending forward to about even 

 with the anterior margin of the first molars. Also, the anterior mar- 

 gin of the posterior narial aperture shows the inflected liplike rim 

 or crest seen in both Meniscotherium and Phenacodus, but this 

 margin does not extend so far forward in the palate as in Menisco- 

 therium. Its anterior margin seems about even with the posterior 

 portion or margin of the last molar. Moreover, the maxillary tuber- 

 osity is much nearer the lateral margin of the narial aperture so that 

 there is only a very small notch between them in contrast with the 

 deep and broadly open saddle in Meniscotherium. 



Basicranium. — The basicranium in Meniscotherium (see pi. 3) 

 appears relatively elongate. This is noticeable in the length of the 

 mesopterygoid fossa and in the posterior position of the occipital 

 condyles with respect to the glenoid surfaces for the mandible. The 

 lateral walls of the mesopterygoid fossa extend posteriorly to dis- 



