346 MR. R. OWEN ON THE OSTEOLOGY OF 
increased power of mastication required for the due action of the large permanent 
teeth. The muscular impressions in the occipital region of the cranium are less strongly 
marked in the Chimpanzee than in the Orang, the occipital foramen is further from 
the posterior plane of the cranium, and its position is less oblique. The lambdoidal 
ridge, the spine of the occiput, and the crista continued from the latter downwards 
towards the occipital foramen, although slightly developed in comparison to the Orang, 
are characters of the adult cranium of the Chimpanzee wihch are wanting in the young 
animal. There is a greater proportion of brain behind the meatus auditorius eaternus in 
the Chimpanzee than in the Orang, and this difference is greater in the adult than in the 
young skull, whence it results that in the former the supra-auditory ridge is at some 
distance anterior to the additamentum suture lambdoidalis, and consequently the skull 
in this respect more nearly approximates the human structure. 
In the young Chimpanzee, the articular cavity for the condyle of the lower jaw is an- 
terior to the bony circle of the meatus auditorius, and on a higher plane ; but, as the zy- 
gomatic arch increases in strength with the increasing power of the maxillary apparatus, 
without any corresponding downward increase of the brain and cranium, the glenoid 
cavity is carried so near to the lower level of the bony meatus, that it no longer, as in 
the young animal and in Man, affords to the condyle of the jaw a support against back- 
ward dislocation. To remedy the effects of this change, a process, of which the rudi- 
ment is perceptible in the young Chimpanzee, co-extends in downward growth with the 
altered position of the articulation of the jaw, becomes interposed between the maxil- 
lary condyle and the meatus, and compensates for the loss of that protection which is 
afforded to the maxillary articulation by the downward development of the cranium 
posterior to the glenoid cavity in the human subject. 
The lower part of the external boundary of the meatus is irregularly jagged in the 
Chimpanzee, for the better attachment of the cartilaginous portion of the auditory pass- 
age. The zygoma is proportionally weaker than in the Orang; the temporal portion 
joins the malar obliquely, and is slightly and irregularly wavy. 
The most characteristic feature of the Chimpanzee’s skull, both in the young and old 
state, is the large projecting supra-orbital ridges, which, being continued into one 
another across the glabella, form a sort of barrier between the cranium and face. 
Behind the junction of the malar with the frontal bone there is a convex ridge leading 
obliquely downwards and inwards, and strengthening the bony septum which divides the 
orbit from the temporal fossa. 
The cranial sutures, which are obliterated in the adults of the Orang, syndactylous 
Ape, and frequently in the adult crania of Baboons and other Quadrumana, are for the 
most part persistent in the Chimpanzee, and the coronal and sagittal sutures have the 
true denticulated structure. The sagittal suture is not continued along the frontal bone. 
The squamous suture is partially lost, but sufficient remains to show that the anterior 
1 Compare Plates LII. and LIV. 

