PEIMATES FEOM MADAGASCAE. 91 



In the following table the transverse diameter of the orbit of Mesoiivopithecus is 

 compared with the corresponding dimensions of Archceolemur, Propithecus, Indris, 

 and Avahis respectively. This is also expressed as a percentage-index of the 

 bi-zygomatic breadth of the skull in each case, 



Arehteokmur. Mesopropithecns. Indris. Propiiheciis. Avahis. 

 Diameter of orbit 29-5 21 23 21 15-5 



,^ , . 1 . , r cliam. X 100 "1 „_ „ 



Orbital index : ^. -^-j ^-p . 27-9 25 37-3 34'2 41-1 



L bi-zygomatic breadth J ^ -xj. j. 



The orbital rim of 3£esoiwopithecus is less raised and everted than in the two 

 modern genera most nearly resembling it in size ; but the postorbital bar is, as stated 

 above, much stouter and stronger. There is the same taming in and extension of the 

 sharp posterior margin of both the frontal and malar portions of this bar as occurs in 

 Palmopropithecus and Archceoleinur. 



The infraorbital foramina occupy a similar position to that seen in Propithecus, 



The shape of the lacrymal bone bears a considerable resemblance to that oi Palmo- 

 propithecus, though it has a smaller extension within the orbit and does not completely 

 enclose the lacrymal fossa. The large size of the raised inner margin of the orbit is 

 again another character recalling Palceopropithecus. The position of the lacrymal 

 foramen can be best described as being in line with the sharp inner anterior margin 

 of the orbit, though the fossa itself is almost entirely within that margin. There 

 is within the orbit a fronto-m axillary suture separating a small os plammi from the 

 lacrymal. The posterior portion of the maxilla forms the floor of the orbit, but 

 does not extend backwards so far as in the case of Archceolemiir, being intermediate 

 both in extent and inclination between the condition of this latter and that seen in 

 Propithemis. 



The Nasal Eegion. — The size and shape of the nasal bones strongly recall the 

 same region in Archceolemur, though, as before stated, the median suture is entirely 

 obliterated in full-grown specimens. The upper part of the fused bones forms an 

 upwardly curved suture with the frontal, the lower outer extremities of this curve 

 nearly coming into contact with the anterior angle of the lacrymal as in Palceopro- 

 pithecus. The lateral margins of the nasals gently curve outwards, this curvature 

 being accentuated towards their anterior extremity in a manner exactly analogous to 

 that noticed in Archceolemur (text-iig. 17), The lower external margin here makes a 

 very short suture with an upward extension of the premaxilla. This condition may 

 be seen in Projnthecus, though apparently not in Indris or Avahis. We have seen 

 that in Palceopropithecus this upward extension of the maxilla is external to the 

 anterior margin of the nasal bones. 



The premaxillse are firmly fused along the middle line almost to the alveolar maro^in. 

 VOL. xvm. — PART II. No. 5. — May, 1908. o 



