CHAP. V] THE CRANIA OF THE SIMIIDAE (PRIMATES) 217 



of importance. For in the female Orang-utan the ridges may remain separated 

 throughout their course, or may barely come into contact with one another, 

 whereas in the male animal, not only may the ridges meet, but they may rise 

 in the form of a crest measuring as much as 10 mm. in height. Posteriorly, 

 the temporal ridges vary too, in male examples meeting the superior nuchal 

 line, and forming a lambdoid crest not seen in female skulls. 



The orbits have an elliptical contour, and the brow ridges are not (as in 

 the African Simiidae) continuous from side to side of the forehead. They are 

 also stouter laterally than medially. The orbital margins are distinct; the 

 lachrymal hamulus vestigial, but there is an elongated lachrymo-ethmoidal 

 suture, since the os planum of the ethmoid though of small vertical extent is 

 somewhat higher anteriorly than elsewhere. 



The spheno-maxillary fissure is a mere cleft of small dimensions, the post- 

 orbital wall being in consequence almost complete. The infra-orbital suture 

 rarely persists long on the facial surface. The nasal aperture is pyriform with 

 upwardly directed apex : inferiorly the nasal margins are quite lost, and no 

 nasal spine is seen, though in some cases it is represented by a median ridge. 

 The nasal bones are more reduced in size than in any other Primate mammal ; 

 usually the conjoined bones form a mere elongated splint, and not infrequently 

 no distinct nasal bones remain : .sometimes a small ossicle at the upper margin 

 of the nasal aperture is all that persists ; the nasal processes of the maxillae 

 then join each other between the orbits. 



The palate is elongated and hypsiloid : the tuber maxillare is variable in 

 development, as is also the post-palatine spine. 



The temporal fossa is deep, owing to the bowing outwards of the zygo- 

 matic arch and the channelling of the alisphenoid. The latter bone touches 

 the parietal, and thus the Orang-utan agrees with Hylobates, Man, and 

 many lower Primates, but differs from the African Simiidae and most of the 

 Catarrhine monkeys : the variations in human skulls in this respect will be 

 described in a subsequent chapter. 



The infra-temporal crest is insignificant. At the base of the skull the 

 shallowness of the glenoid fossa is to be remarked, but as was noted in 

 describing the cranium of Hylobates, this shallowness is not to be regarded 

 as related to lateral movements of the mandible, which are limited by the 

 excessive development of the canine teeth. Movements in an antero-posterior 

 direction may possibly occur and may produce some effect as regards the 

 glenoid surface. The endoglenoid process or tubercle is small, as is the 

 styloid process, which is often absent. The vaginal process is also undeveloped. 

 Anomalies about the margin of the foramen magnum are not common, though 

 the ossification of the adjacent part of the suspensory ligament sometimes 

 leaves a spicule of bone at the anterior margin. As regards the endocranium, 

 a distinction between the Orang-utan and the two African Simiidae was 

 pointed out by Huxley. In the Orang-utan the cribriform plate of the 

 ethmoid articulates posteriorly with the pre-sphenoid, as in Man. In the 

 Chimpanzee and Gorilla these two bones are separated superficially by flange- 



