108 DE. H. r. STANDING ON SUBFOSSIL 



frontal lobes ; and the hemispheres leave the cerebellum uncovered. The occiput 



forms a plane at right angles to the axis of the skull and the occipital condyles are 



vertical. The facial region is greatly developed, large frontal and maxillary sinuses 



occurring in the adult. The face, indeed, is rather suggestive of a Ruminant than of a 



Lemur. The lines of attachment of the temporal muscles form a sagittal crest, as in 



some of the fossil Lemurinse and Indrisidae. There are also strong lambdoidal crests 



continuous with the high zygomatic processes of the squamosal. 



One peculiarity in which the Megaladapinse differ from almost all the recent and 



fossil Lemuroids is their great interorbital breadth. This breadth may be conveniently 



, . , „ f .3 ^1 interorbital breadth x 100 



expressed m the lorm 01 an index, tnus : ■. j rr — ,. , ^ • 



" maximum length 01 skull 



Measurements taken on a series of Lemuroid skulls, recent and fossil, give the 

 following results : — 



per cent. 



Chiromys madagascariensis 31'1 



Megaladapis grandidieri 28'3 



Indris brevicaudatus 20"8 



Propithecus diadema 18'6 



Avahis laniger ..18 



Mesopropithecus pithecoides 17'8 



Palceopropithecus maximus 17'3 



Lemur jullyi 15'4 



Perodicticus potto 14'8 



Lemur varius 14'5 



Archceolemur edwardsi 13'5 



Lepilemur , . . 11'4 



Nycticebus ............... 8'5 



It is interesting to note that a quite young skull of Megaladapis grandidieri has an 

 interorbital index of only 18-1, in this respect ranging itself with the various sub- 

 divisions of the Indrisinae, It is thus evident that the great interorbital breadth of 

 the adult Megaladapis is a secondarily acquired character. 



The orbits in all three species are small and tubular and are directed outwards, the 

 plane of the orbital rim being nearly vertical. The lacrymal foramen is situated 

 without the orbit or in line with the orbital margin. No postorbital wall occurs, and 

 the hinder edge of the postorbital bar is rounded. The nasalia are strongly 

 developed and at their anterior extremity are (in the two species where this part of 

 the skull is known) prolonged in a downward direction into a curved beak-like form. 

 Auditory bullae are present, but in none of the species take the prominent inflated 

 form so characteristic of the majority of Lemurs. 



The zygomatic arches are high and strong, contrasting with the light thin arcades 

 of existing Lemurs; and they do not curve widely away from the skull, as is the 

 case with Palceopropithecus and Mesopropithecus. 



