Satyrus adrotes, Meyer, Arch. f. Naturg., p. 182 (1856).
Simia gorilla, Schl., Mus. Pays-Bas, vii., p. 8 (1876).
Gorilla mayema, Alix et Bouv. C. R., lxxxv., p. 58 (1878).
(Plate XL.)
Characters.—The face of this massive and most ponderous of all the Apes is naked and black, very wide and elongated. The large head has a ridge of hair along the central crest, and its lower jaw is very wide and far extended backward. The nose is long and high, and broad and flat at its extremity, and is also grooved longitudinally. The muzzle is broad, the mouth wide; the upper lip short, and the lower mobile and protrudable. The eyes are large; the ears naked and black, with the posterior upper angle pointed, and the lower margin produced into a rudimentary pendulous lobule.
The cranial region is comparatively small. The supra-orbital ridges, in which the eye-brows are set, form, from their prominence, a marked feature of the face. They overhang the eyes, causing them to appear very much sunk in the skull. The neck is short, the chest and shoulders wide, thickly haired and suggestive of great strength.
The arms are much longer than the fore-arms, and the feet, which have no in-step, exceed the hands in length, and are much broader than in other genera of the Simiidæ. The heel, which in the Orangs is small, is in the Gorilla strongly developed, on which account it can easily stand erect. Its opposable great-toe is large and flattened, and has a wide nail; while the lower joints of the second, third, and fourth toes—which are also short and thick—are united by a web. The arms, on which the hair converges on both sides of the joint towards the elbow, are so long as to reach down to the middle of the leg when the Gorilla stands erect. The thumb is short and thick, and is tipped with a broad nail. The hand is broad, thickly haired on the back, and wrinkled from the wrist to the fingers. The fur of the Gorilla consists of long, thick, straight, or stiffly curved bristles, beneath which is a shorter curled woolly hair, or under-fur.
The skull of the adult male has very protruding jaws, and enormous supra-orbital ridges. The cheek-bones are broad; the temporal muscles meet along the top of the cranium, and have enormous bony crests for their attachment. The same is the case on the back of the head for the powerful neck-muscles. The true form of the skull is obscured by these great ridges and by the extent to which the face protrudes. The brain-case is better shaped internally than appears externally. The orbits have the same form as in Man.
The canine teeth are enormously developed. The upper molars are four-cusped, and have the oblique ridge, already often referred to, from the front inner to the hind outer cusp, the posterior of the three being much larger than the other two, a character distinguishing its jaw from that of Man and the Chimpanzees. The anterior lower molars have five cusps, three on the outer side and two on the inner, as in Man.
The lower jaw has no true chin, and its symphysis is very long and quite different from what is seen in the human symphysis. The opening for the passage of the spinal cord is situated in the posterior third of the base of the skull, and not, as in Man, nearly in the centre.