16 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 67 



fragile condition. Hence one can not be certain what modifications 

 were present around the ectal orifice of the optic nerve near the base 

 of the supraorbital process of the frontal. Both frontals appear to 

 have developed thin plates. It is possible that they may have 

 curved below the optic nerve in the same manner as in Platanista. 

 This point can not be settled on the basis of these two skulls alone. 



In the preceding paper * attention was called to the presence of 

 a peculiar shelf in the temporal fossa above the upper margin of the 

 squamosal. It is nov/ apparent that this shelf was the result of 

 crushing and tlie consequent buckling of the bones involved and that 

 it is not comparable with a similar groove on the skull of Platanista. 

 The second skull has suffered in the same way on the right side, but 

 to a lesser degree. 



At the base of the falcate process of the basioccipital and near the 

 posterior margin of the alisphenoid is the partially closed ectal 

 orifice of the canal for the carotid artery. The mandibular branch of 

 the fifth cranial nerve issues through a cleft on the posterior border 

 of the alsiphenoid at a point 11 mm. external to the orifice of the 

 carotid canal and on its forward and outward course crosses the 

 ventral face of this bone, finally emerging in the temporal fossa 

 through the foramen ovale. 



A postero-external process of the alisphenoid projects backward, 

 meeting the squamosal along its external border, abutting against 

 the exoccipital posteriorly, and uniting with the underlying process 

 of the basioccipital internally. The alisphenoid and the above 

 mentioned bones form the fossa in which periotic and tympanic 

 bones are lodged. A small foramen pierces the alisphenoid above 

 the anterior process of the periotic. Two large foramina appear in 

 this fossa above and internal to the jugular incisure. The ectal orifice 

 of the internal foramen is situated internal to the jugular incisure; it 

 opens at the base and near the posterior margin of the falcate process 

 of the basioccipital. This foramen probably represents the com- 

 partment for the nerves in the foramen lacerum posterius. The 

 external foramen is partially inclosed by the exoccipital and may 

 aft'ord a passage for the jugular vein. The foramina within the 

 tympano-periotic fossa have the same general arrangement as on one 

 skull of Eurhinodelfhis hossi ^ which was also obtained from the 

 Calvert formation. In skulls of Platanista, Inia, and Lipotes, a large 

 fissure occupied the area corresponding to the tympano-periotic fossa 

 on the Zarhachis skull. 



« KeUogg, R., Proc. U. S. Nat. Mus., vol. 63, pp. 18-19. 1924. 



• R. Kellogg, On the occurrence of remains of fossil porpoises of the genus Eurhinodelphis in North 

 America. Proc. U. S. Nat. Mus., vol. 66, publ. 2563, pi. 5. 1925. 



