350 



PEOF, G. ELLIOT SMITH ON THE 



ill which the roof of the cranium had been removecl by a clean saw-cut. This I shall 

 adopt as a type. 



The cerebral hemispheres were 52 mm. long, 40 mm. broad («. e. 20 mm. each), and 

 approximately 34 mm. deep. 



The olfactory bulbs must have been almost, if not quite, completely overlapped 

 l)y the hemispheres ; and about as much of the cerebellum was exposed as is the case in 

 the genus Lemur. 



The orbital excavation extends back as far as the lower end of the Sylvian fissure ; but 

 it does not extend upward to so gi*eat an extent as in Lemur. 



Iig.22. 



SCO. 



sp 



Fig. 22. — Propithecns diiidewa. Plan of the dorsal surface of the brain. Nat. size. 

 Fig. 23. — Propithenis diadema. Left lateral aspect of same. 

 Fig. 24. — Eight lateral aspect of same. 



The rhinal fissures are much more extensive aud compk'te than they are in any other 

 subfamily 9i Lenuu's (excejiting the Galagos), as is well shown in Milne-Ed wards's and 

 Grandidier's illustrations (' Histoire de Madagascar,' (2) tome vi. pi. 86. figs. 2 & 3). 



The Sylvian fissure does not differ from that of Lemur. In this, as in most of the 

 examples of Propithecns examined (compare also Milne-Edwards's pL 86. figs. 1 &, 3), 

 the upper extremity of the suprasylvian sulcus is strongly curved backward, being 

 obviously united to the small sulcvis (d) which is intercalated between the upper ends of 

 the Sylvian and postsylvian sulci in most Lemurs. 



There is a typical postsylvian sulcus, the upper end of which is bent forward (in 

 varying degrees) in all cases. There is a clearly-defined orbital sulcus placed alongside 

 the olfactory bulb. It is subject to great variations in form. On the left hemisphere 

 of this and every other brain which I examined (although Milne-Edwards's case is an ex- 

 ception, op. cU. pi. 86. fig. 3) the simple primitive linear form of the sulcus is maintained; 



