148 



DE. H. F. STANDING ON SUBFOSSIL 



the broadening of the internal posterior edge of the orbital bar in both a vertical and 

 horizontal direction. This inner edge is often so thin as to be quite translucent. 



The extent of this apparently vestigial septum is disguised by the fact that the 

 postorbital bar is triangular in section. If the actual internal measurement from 

 the orbital rim to this sharp edge be expressed as a fraction of the transverse diameter 

 of the orbit, in the case of Archceolemur j)latyrrM,nus it is 47'8 per cent., in Mesopro- 

 pithecus 36-8 percent. Similar measurements taken in a horizontal direction from the 

 inner anterior margin of the orbit to the posterior edge of the postorbital septum, 

 and expressed as a fraction of the transverse diameter of the orbit, give in the case 

 of CJiiropotes 25 per cent., and in the case oi Nyctipiihecus 47 per cent. 



The Occipital Region. — That the arrest of brain-evolution and actual loss of 

 cerebral substance in the Malagasy Lemurs should have entailed other retrogressive 



Text-fiff. 42. 



Inclination of the occipital plane of young Mesopropithecus (A) compared with that of 

 Alouatta helzehul (B). 



changes is not to be wondered at. The vertical occiput which is seen in the adult 

 Megaladapis and Palceopropithecus is probably an instance in point. It is note- 

 worthy in this connexion that the young of all the Lemurs appear to have the 

 occipital plane much more inclined than the adult. That a vertical occiput may, 

 however, be a secondarily acquired character depending on a massive mandible or on 

 some peculiarity of the vocal organs is seen in the case of Alouatta (see text-fig. 42). 



Long narrow occipital condyles have been mentioned by certain writers as a 

 Lemuroid feature. We have seen in the case of several of the subfossil forms 

 described in this memoir that the condyles are broad and rounded in shape, con- 

 forming rather to the " Anthropoid " than to the " Lemuroid " type (see text-fig. 43). 

 A conspicuous convexity for the lodgement of the vermis of the cerebellum is found in 

 the extant Lemurs, and has been mentioned as a characteristic feature. This is 

 absent, at any rate in the adult, in Archceolemur edtvardsi, Faloeopropithecus, and 

 Mesopropithecus. 



