IN THE EXTINCT LEMUES OF MADAG-ASCAE. 



173 



It is very unfortunate that the patterns of the sulci in this cast are more blurred and 

 indistinct than in the other two casts (those of Lemur jullyi and Meso^rojiUhecus), the 

 resemblance of which to living genera renders the plan of the convolutions of less interest. 

 However, sufficient can be seen of the furrows (or, rather, of the irregularities 

 resulting from their presence) to enable us to map out the main features of their 

 arrangement. 



The hemispheres were 72 mm. long, 59 mm. (?'. e. 29'5 each) wide, and 50 mm. 

 deep. 



The olfactory peduncles were narrow and elongated, like those of 3£egaladapis ; but, 

 without having seen the skull, I am unable to make any detailed statement on this 

 point. The large cylindrical masses representing the maxillary and ophthalmic 

 divisions of the trigeminal nerve prevent us from determining the position and relations 

 of the optic chiasma, which are so peculiar in Megaladapis. However, this is a matter 

 which the describer of the cranium can at once determine. 



The anterior end of each hemisphere is blunt and rounded, as in Chiromys and 

 Megaladapis, though in a lesser degree. The orbital area is very small, but there is a 



Text-fif'. 62. 



S- iji^ apar. 



^iip. 



s- fi-ont. C'if.-\-— 



buii.ou: 



■ cerebeUian/. 



s. 07-b. s.ps. lob. floe-. 



Left lateral aspect of the brain of QMromijs madagascarensis. Natm-al size. 



definite orbital margin, which has disappeared in the other two genera just mentioned. 

 The retention of even this small orbital margin distinctly enhances the resemblance 

 to the other Prosimise and enables us to interpret the features of the brain of Chiromys 

 and Megaladapis with more certainty. Almost the whole length of the orbital surface 

 is occupied by a deep orbital sulcus, and immediately above the orbital margin is the 

 anterior end of the inferior frontal [coronal] sulcus. After examining such a brain as 

 this it is easy to understand how, when the orbital margin is wiped out and there is 

 nothing to prevent the confluence, the orbital sulcus joins the inferior frontal [coronal], 

 as I have described and figured (i, figs. 33, 34, 35, and 36, pp. 356 and 857) in the 

 case of Chiromys. It is not possible to say for certain whether or not the 



2a2 



