The Macaques live in India, Tibet, North and South China, Japan, and southwards, and in some of the great islands of the Archipelago, Formosa, in Africa, in Barbary, but not south of the Atlas range, and in Europe, on the Rock of Gibraltar.
They all have cheek-pouches and callous pads, or callosities, on their seat, and thus resemble the Guenons; moreover, most of them have throat or laryngeal sacs, which open into the membrane above the vocal organ and below the base of the tongue (in the thyroid membrane).
On examining their jaws it will be noticed that there is the same number of teeth as in the other Monkeys already described, and that the upper eye or canine tooth on each side is very strong and long. Now, these teeth are not for killing or stopping living prey, although their possessors do not hesitate to snap up a good-sized Beetle, a small Lizard, or even a Frog, but they make, with the first false grinder of the lower jaw, a capital nut-opener. The canine, when the mouth is shut, fits just in front of this tooth, which is usually called the first pre-molar, and which is pressed back and made to slant in the jaw by the constant pressure and movements of the canine. The back of the canine is sharp, and comes in contact with the equally sharp edge of the slanted pre-molar below, so that when a nut comes between the two it is cut and crushed at the same time. The canine does not thus fit into a diastema, or vacant space, but is of great use to the animal. This arrangement is interesting, because it produces a distortion of the front back teeth of the lower jaw for a definite and useful purpose: it is noticed in some of the Guenons, and is particularly seen in mouths of the great Baboons, which will be noticed further on.
The other back teeth resemble somewhat those of the Guenons, but the last one of the lower jaw has five cusps, or prominences, on it.
All these Monkeys going very readily on all-fours have several interesting modifications of the structures observed in the climbing Monkeys, but of course their general construction is the same. They have not, however, the pouched stomachs of the Semnopithecus, and their nearest resemblance is to the African Guenons.
Like all the Monkeys which are lower in the animal scale than the great man-shaped Apes, the Macaques have narrow wrists, long linger bones, and a short and backwardly-placed thumb. There are nine bones in the wrist. The hip-and haunch-bones are long, and the first are hollowed out, and their direction refers to the method of progression on all-fours, and their general appearance is rather that noticed in the regular four-footed beast of prey, and they differ much in breadth relatively to those of man.
The length of the tail depends upon the number of the tail-pieces, or vertebra, and upon their size. In the Gibraltar Ape there are only three of these caudal vertebræ, but in the Bhunder there are fifteen and sometimes eighteen in the tail, which measures nine inches, whilst in the Pig-tailed Inuus there are seventeen. It appears that some of the long-tailed kinds have no more vertebræ than the others, but that the diminished length is due to their shortening. The long and middle-sized tailed kinds have chevron-or Y-shaped bones under the tail, and the nature of these has been explained already.
Living upon a great variety of food, and using their jaws with rapidity, these Monkeys are furnished with a curious modification of a muscle, which exists in man and the higher Apes. There is in these a muscle on each side of the throat, which draws the chin down, or, in other words, helps to open the mouth. It is called the two-bellied, or digastricus muscle, as it has two muscular masses—one attached to the lower jaw, and the other to the lump of bone behind the ear—and they are united by a thin tendon. This tendon is attached to the side of the bone at the base of the tongue, or os hyoides, and it passes through a loop of a muscle which passes from the ear-bone (styloid process) to the os hyoides. The muscle acts as follows:—When the mouth is to be opened after swallowing, the base of the tongue-bone is pulled down by a muscle which comes from the breast-bone to it, and then the front belly, or muscle of the digastricus, pulls from the base of the tongue against the lower jaw and drags it open. But when the muscle relaxes, and the jaw is shut preparatory to swallowing, the digastricus begins to assist in this operation. In swallowing, the base of the tongue is drawn upwards towards the roof of the mouth, and the back and front bellies of the muscle now under consideration drag on their fixed tendon, and straighten, so as to assist in this.
In the Macaques, this tendon is replaced by muscular bands, and greater vigour is given to the muscle, so that the jaw is pulled at more rapidly, and the tongue is elevated with energy.
As there is a greater power given in drawing up the tongue in the first stage of swallowing, there must be something extra to pull it down again in the second stage, for in this the back of the throat, the gullet, and the back of the tongue are all brought from above to a lower level. This is arranged by a modification of a muscle, which in man and the Chimpanzee, for instance, stretches from the top of the bladebone, across the lower part of the neck, to the bone at the base of the tongue (the omo-hyoid muscle). It has also two bellies in man, or, in other words, the muscular fibres are attached to the bladebone and to the hyoid bone, and there is an intermediate tendon; moreover, this passes through a pulley, so that the obliquely-placed muscle in the lower part of the neck acts straight upon the tongue, and pulls it down in a right line. In the Macaques, this muscle has no central tendon, and the muscular fibres pass all the distance from the bladebone to the os hyoides at the base of the tongue.