Habits.—The Proboscis Monkey, variously called Blanda (or White Man) and "Rasong" by the natives, is an arboreal creature living in small troops. "As usual," writes Mr. Hornaday, "they were over water, and, being swift climbers and quite shy, were hard to kill. I saw altogether, during my ramblings in the forests of Borneo, perhaps a hundred and fifty Proboscis Monkeys, and, without a single exception, all were over water, either river, lake, or submerged forest. As long as they are in sight they are very conspicuous objects, choosing the most commanding positions in open tree-tops. Once I saw thirteen in one tree, sitting lazily on the branches, as is their habit, sunning themselves and enjoying the scenery. It was the finest sight I ever saw in which Monkeys played a part. The cry of the 'Blanda,' is peculiar and unmistakable. Written phonetically it would be 'Honk,' and occasionally 'Kec-honk,' long drawn and deeply resonant, quite like the tone of a bass viol.... The Proboscis Monkey is a large animal of striking appearance both in form and colour. Taken altogether, Nasalis larvatus is, to the hunter-naturalist, a very striking object of pursuit, and were he not partially eclipsed by the Orang he would be the most famous Quadrumane in the East Indies."
THE MAN-LIKE APES. FAMILY SIMIIDÆ.
In this family are included the Gibbons, the Orangs, the Gorillas, and the Chimpanzees, the most highly organised and the nearest to Man in structure of all the Anthropoidea. To these groups the term "Ape," has been by many writers chiefly restricted, the remaining families of the Old World, and all of the Western Hemisphere, being designated "Monkeys" as a convenient method of nomenclature. The outward resemblance of the Simiidæ to Man has made the various members of the family objects of the greatest interest, not alone to the naturalist, but to every intelligent person; and has naturally suggested a constant inter-comparison between the characters of both.
They are all essentially arboreal climbing animals, yet when they come to the ground they progress in a semi-erect position of their own accord. Their front-limbs are always so much longer than their hind-limbs, that when walking on a level surface their fingers reach the ground, without stooping lower than their semi-erect attitude. Their front-limbs vary in length in the different genera; so does the thumb; but their great-toe is always smaller in proportion to the foot than it is in Man, and, unlike his, is opposable to the other toes. As they belong to the Catarrhine group, their nose has a narrow partition between the nostrils, which are directed downwards. In all, an external tail, cheek-pouches, and (except among the Gibbons) ischial callosities are wanting. All are covered with hair, some more thickly than others, but no Ape has on its head the long abundant locks which Man possesses.
The form of the skull varies very greatly in the Simiidæ. It is, however, always longer than broad. In its frontal region it is never so rounded and elevated as in Man. The roof of the eye-sockets projects into the fore part of the brain-cavity, and considerably reduces its capacity. The pre-maxillary bones (carrying the incisor teeth) are relatively more distinct and much larger than in Man, "the sutures separating them from the maxillary bones remaining visible after the adult dentition has been obtained." (Mivart.)[[1]] The Simiidæ have a bony meatus or canal to the ear. The back part of the head, which among the Guenons is flat, is convex among the Simiidæ. The palate is long and narrow, and the margins of the jaws nearly parallel. The lower jaw is always in one piece, the two halves being firmly ossified in the middle. The dental formula of the Man-like Apes is I22, C11, P22, M33 (i.e., 32 teeth in all); their inner upper incisors are larger, and the lower are smaller than the outer pair; the canines are large, and between them and the neighbouring incisor above there is a vacuity (or diastema), and, below, between them and the nearest pre-molar. The upper pre-molars have three roots, and the lower, two; the upper molars have four tubercles, their crowns being relatively wide; the lower molars have five tubercles, but the posterior has no hind talon.
The opening for the passage of the spinal cord is situated towards the posterior portion of the base of the cranium, and is thus further from the centre than in Man.
Except among the Gibbons, the vertebral column shows in the sacral region indications of that curve—or concavity in the back between the two convexities of the neck and loins—which is one of the distinctive characters of the human skeleton. The processes for the interlocking of the vertebræ, which are large in the lower Anthropoids, are much reduced in the Man-like Apes, and become inconspicuous in Man.
The breast-bone is flat, and resembles that of Man, and, in all, except the Orang, is composed of two bones. The arm-bone is often shorter than the fore-arm. The radius and ulna can be completely rotated. The articulating surface of the trapezium, the wrist-bone (carpus), to which the thumb is attached, has a rounded face like that of the ento-cuneiform bone in the ankle (tarsus), a form which, as already pointed out (Vol. I., p. [11]), was in the Lemuroids correlated with an opposable great-toe, so here it is correlated with a true opposable thumb. In the Monkeys and Lemuroids this bone is not generally rounded, and they have not the thumb opposable in the strict sense that it is among the higher Apes.
The thigh-bone (femur) is shorter than the arm-bone (humerus); and the foot is very long; yet the absolute length of the tarsus is never so great as in Man; it is the rest of the foot which is so much longer relatively in Apes. The ento-cuneiform, or articulating bone of the ankle for the great-toe, has a sub-cylindrical surface, which gives a great range of motion to that digit, towards and from the plane of the foot.
The brain of the Apes closely resembles in general form and structure that of Man; but the cerebral hemispheres differ in being much elongated and depressed, and the cranial capacity of the skull, which is never less than 55 cubic inches in any normal human subject, is in the Chimpanzee 27½ cubic inches; in the Gorilla 35 inches; in the Orang 26 inches; and in the Gibbons very much less. The cerebrum has its surface richly convoluted; and its posterior lobes always entirely over-arching the cerebellum, except in the Siamang (Hylobates syndactylus).