PRIMATES FROM MADAGASCAR. 77 



though approaching more nearly to the condition of recent Lemurs than is the case 

 with Megaladcqns (Plates XII. & XIII.). The upper lines of attachment of the 

 temporal muscles form strongly marked ridges, occasionally uniting in old skulls to 

 form a longer or shorter sagittal crest ; but in the majority of cases the fusion of these 

 ridges has only taken place for a short distance above the occiput, the two lines 

 diverging at various angles, leaving a flattened space, wedge-shaped or fusiform, 

 according to the direction taken by the lateral ridges before they widely separate to 

 join the postorbital bar (Plate XIII,). The parietal suture becomes obliterated in old 

 specimens, though the line between the frontals can be traced in almost every case. 

 The squamosal extends up the wall of the brain-case to about the same relative height 

 as in jPropithecus, and the spheno-parietal and coronal sutures closely conform to the 

 conditions observed in the extant genera, though the coronal suture has an acute wedge- 

 shape form recalling that of some of the Cebidse (e. g. Pithecia rujiventer) (text-fig. 9). 



Frontal Begion. — The postorbital region of the frontal resembles the corresponding 

 part of the skull of Megaladapis, being very much constricted compared with the 

 modern representatives of the subfamily. The average breadth in this region for 13 

 skulls was 36 mm. (max. 405, min. 28). This is about 18 per cent, of the maximum 

 length of the skull, being only about half a similarly obtained index in the case of 

 Projnthecus, viz. 35 "6. 



The frontal sinuses are voluminous and have encroached on the cranial cavity in a 

 manner analogous to that observed in Megaladapis. There is indeed a similar though 

 less pronounced atrophy of the temporal lobes of the brain with a partial obliteration 

 of the lumen between the cerebral and olfactory fossee*. The median line of the 

 frontal behind and between the orbits is convex, though the degree of convexity varies 

 greatly in different specimens. There is also a slight convexity in a transverse 

 direction. 



The Orbital Region. — The size, position, and direction of the orbits have already 

 been referred to as differentiating Pali^ojn-ojnthecus from living Indrisin^. These 

 characters must now be considered more in detail. In size the orbits are pro- 

 portionately smaller than in any of the recent representatives of the subfamily, and 

 indicate an animal of diurnal habits. A percentage-ratio, comparing the transverse 

 diameter of the orbit with the bi-zygomatic breadth, gives the number 23. Similar 

 indices in the case of Propitliecus, Indris, and Avahis respectively give 34-2, o7'3, and 

 41. Except in quite young skulls the margin of the orbital process of the frontal is 

 raised to form a strong bony rim, which is continued around the external and anterior 

 margin by a similar growth of the malar. The latter bone attains an extraordinary 

 depth and breadth below the orbit. The distance measured from the external anterior 



* For further details the reader is referred to the report by Dr. Elliot Smith ou the brain-casts of 

 Falcwpropiiliecus and other recently discovered Primates published as an appendix to the present memoir. 



.\l2 



