2.6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



tine foramen is nearly confluent with the sphenopalatine foramen 

 somewhat as in M eniscotherium, and both are above and a little for- 

 ward of the notch in the posterior margin of the palatine between 

 the maxillary tuberosity and the ascending plate of the palatines. 

 In Phenacodus, however, these foramina are posterior to M 3 , whereas 

 in M eniscotherium they are anterior to the posterior margin of the 

 tooth series. 



The optic foramen is relatively closer to the sphenoidal fissure in 

 Phenacodus, the actual distance being approximately the same as 

 or somewhat less than in much smaller skulls of M eniscotherium 

 and Ectocion. Also, the anterior opening of the alisphenoid canal 

 seems more closely appressed and immediately lateral to and some- 

 what lower than the sphenoidal fissure in Phenacodus. In the 

 material observed I have been unable to determine whether there 

 is a foramen rotundum confluent with the anterior opening or whether 

 the second branch of the trigeminal nerve passed through the sphenoi- 

 dal fissure with the first as Simpson (1933) has suggested. I sus- 

 pect that these nerves emerged separately as seems demonstrated in 

 M eniscotherium, although they possibly left the cranial cavity to- 

 gether through a posterior confluence of the foramen rotundum and 

 sphenoidal fissure. The Cope endocast of Phenacodus is ambiguous 

 in this respect, as the two sides are not alike in this area. 



In Uyopsodus the orbital plate of the maxilla appears relatively 

 short and wide with the long diameter nearly transverse, and the 

 sphenopalatine foramen is about even with or slightly posterior to the 

 hind margin of the last molar. The optic foramen is well in advance 

 of and a little higher than the sphenoidal fissure. As observed in 

 Phenacodus, it is just ahead of the anterior extremity or angle of 

 the crest which forms the inferior border of the temporal fossa — the 

 forward extension on the cranium of the anterior root or crest of the 

 zygomatic process of the squamosal. In M eniscotherium this crest 

 is not so well defined and does not coincide with the ledge or bulge 

 immediately above the sphenoidal fissure which it forms in Phena- 

 codus and Hyopsodus. The alisphenoid canal, if correctly inter- 

 preted for Hyopsodus, is decidedly elongate and the anterior open- 

 ing, presumed confluent with the foramen rotundum, is somewhat 

 less distinctly lateral to the sphenoidal fissure. It appears as a 

 marked elongation or extension posteroventrally of the opening of 

 the sphenoidal fissure. 



Occipital view. — In an occipital view the most striking feature of 

 M eniscotherium is the overhang of the occipital crest which con- 



