In the lake region south of the river they are fairly abundant as far south as the head-waters of the Rembo Nkami and through the low country of the Esyira tribe, but they are very rare in the forests, and unknown in the highlands and plains of this country. South of the Chi Loango they are quite unknown, and south of the Congo never heard of. There are no means possible to estimate their number, but they are not so numerous as may be supposed, and from the reckless slaughter of them by the natives in order to secure them for white men, they may soon become extinct. Their ferocity alone has saved them up to this time from such a fate, but the use of approved arms will soon overcome that. The skeleton of the gorilla is so nearly the same as that of the chimpanzee, which has elsewhere been compared to the human skeleton, that we shall not review the comparison at length, but must note one marked feature in the external form of the skull, which differs alike from other apes and man. The skull of the young gorilla is much like that of the chimpanzee, and remains so until he approaches the adult state; but as he approaches this period, the ridge above the eyes becomes more prominent, and at the same time a sharp, bony ridge begins to develop along the temples, and continues around the back of the head on that part of the skull called the occiput. At this point it is intersected by another ridge at right angles to it. This is called the sagittal ridge, and runs along the top of the head towards the face; but on the forehead it flattens nearly to the level of the skull, and divides into two very low ridges, which turn off to a point above the eyes and merges into that ridge. These appear to be a continuous part of the skull, and are not joined to it by sutures. The mesial crest in very old specimens rises to the height of nearly two inches above the surface of the skull, and imparts to it a fierce and savage aspect; but in the living animal the crests are not seen, as the depressions between them are filled with large muscles, which make the head look very much larger than it would otherwise. These crests affect only the exterior of the skull, and do not appear to alter the form or size of the brain cavity, which is larger in proportion than that of the chimpanzee. These crests are peculiar to the male gorilla, and the female skull shows no trace of them. [Illustration: PLATE I] [Illustration: PLATE II]