8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



Lemur which extends from the inferior petrosal sinus to its posterior 

 opening adjacent and essentially confluent with the condylar foramen. 

 Except for relative proportions, the cranial circulation noted in the 

 vicinity of the petrosal was essentially like that in modern lemurs. 



Ventral surface. — The shortness of the rhinencephalon and wide 

 spacing of the prominent, ovate pyriform lobes is particularly evident 

 in the ventral view of the cast. The rhinencephalon tapered sharply 

 forward toward the roots of the olfactory lobes that are missing on 

 the cast. It is of interest to note that the diameter of the posterior or 

 basal portion of the olfactory roots, partially represented on the cast,, 

 appears relatively unreduced in comparison with many later primates, 

 suggesting retention of the importantly developed sense of smell. A 

 transversely elongate ridge, slightly concave forward and truncated at 

 each end represents the optic chiasma with its pedicles for the optic 

 nerves at the rather widely separated lateral extremities. Its position 

 is near the olfactory roots and about in line with the anterior margins 

 of the pyriform lobes. Widely spaced crests including representation 

 of nerves III to VI (except V 3 ) bound medially the form of the 

 anterior part of the pyriform lobes. These originate just anteromedial 

 to the pedestal representing the foramen ovale and extend forward 

 nearly to the position of the optic nerve, although the crest on the 

 left side of the cast is broken partway back. Separation between the 

 contents of the sphenoidal fissure and foramen rotundum (V 2 ) is not 

 evident in the cast, although these foramina are distinct, opening 

 close together and close to the optic foramen in the orbital fossa of 

 the skull. 



In almost the exact center of the ventral surface of the cast repre- 

 sentation of the hypophysis or pituitary body, with its midpoint about 

 7]/2 mm. posterior to the anterior margin of the optic chiasma, is 

 seen as a small, ventrally protruding, nearly hemispherical structure. 

 Its posterior margin superiorly is rather sharply deflected and ap- 

 pears slightly "undercut" by bony projections, the posterior clinoid 

 processes of the basisphenoid. Posterior to this there is slight damage 

 to the cast but the superior surface of the basioccipital and basisphe- 

 noid posterior to the clinoid plate and between the inferior petrosal 

 sinuses shows no important deviation from a relatively even surface. 

 There is no indication of the pons as a distinct structure other than 

 a gentle longitudinal convexity not separately defined or distinguished 

 from the inferior surface for the medulla oblongata. A small projec- 

 tion on the cast, however, is observed immediately posterolateral to 

 the position of the hypophysis and about at the anterior extremity of 



