190 LLOYDS NATURAL HISTORY. 



in the Gorilla, and the back of the head convex.* The central 

 (sagittal) crest, so strongly developed in the Gorilla and the 

 Orang, is here wanting ; the supra-orbital ridges which extend 

 across the face, and the occipital prominences for the back- 

 muscles, though large, are also less marked. The orbits have 

 a circular rim, and are less prominent than in the Gibbons, 

 The nasal bones are but slightly arched, and the openings for 

 the nostrils round and small. The jaws, which are smaller, 

 proportionately to the cranium, in this genus, than in any other 

 of the Simiidce^ protrude far forward, but the symphysis of 

 the lower jaw is smaller than in the Gorilla, and its two halves 

 low and wide. The bones of the skull are much hollowed 

 out into cavities (sinuses) in the forehead, nose, and jaws, all 

 of which communicate with each other. The plane of the 

 foramen magnum (for the passage of the spinal cord) is oblique 

 to the plane of the base of the skull. 



The volume of the cranium is from twenty-six to twenty- 

 seven cubic inches, or about one-half of the lowest capacity 

 of a normal human cranium. A styloid process is more or 

 less distinctly visible in the Chimpanzees. 



The canine teeth are long and conical, but less than in the 



Gorilla; and the diastema, or gap, between them and their 



neighbouring teeth is smaller than in the other Apes. The 



molar teeth are four-cusped, and have the oblique ridge already 



described extending from the front inner to the hind outer cusp ; 



and the middle lower molar has five cusps, both these dental 



characters being similar to those in Man. The anterior lower 



pre-molar, however, is pointed, and has a long sharp anterior 



edge, as in the Cercopithecida. 



* The deformity known in the human skull as acrocephaly, which occurs 

 in all races of men, and is due to the too early ossification of certain of its 

 sutures, has been found in the Chimpanzee. 



