A Hand-book to the Primates, Volume 1 (of 2)

by Henry O. Forbes

Distribution.—This species is at present known only from Fort Dauphin in the south-east of Madagascar. [Type in British Museum.]

THE ENDRINAS. SUB-FAMILY INDRISINÆ.

This, the last sub-family of the Lemuridæ, is considered to contain the highest members of the whole Sub-order. They are distinguished by having their fur abundant, longer and woolly above, shorter beneath, with the hands and feet haired to the tips of the digits. Their head, set at right angles to the spinal column, is rounded, the face elongated and naked, with a deep furrow separating the nostrils. The eyes are large, and have a third eyelid, or nictitating membrane, to draw across the pupil during the day. The ears, which are naked inside and fringed on the outside, are moderately long and buried in the fur, but are less movable at will than is the case with the Galagos. Their fore-limbs are much shorter than the hind ones. The arms, which are united to the body by a parachute-like fold of integument, have long, narrow, and strong hands, of which the thumb is short, set far back, and but little opposable. The rest of the fingers, except the index, which is short, are long and slender, and terminate in a round disc. The feet are elongate, and the great toe, which is freely opposable to the other toes, is very large and broad, being, indeed, nearly as wide as the rest of the digits together; the remaining toes are united by a membrane as far as the second segment. The females have the mammæ situated on the breast.

In the skull the facial region is relatively small, and the cranial region relatively large. The external nostrils communicate with a cavity on the underlying bone; the pre-maxillary bones are deeply excavated in front, and the anterior perforations in the bony palate, behind the incisor teeth, are large. The lower jaw has its angle large, produced backwards, the line of union of its two halves being long, and its lateral movements very limited. In regard to their dentition, the number of the milk-teeth in the young individual is greater than that of the permanent set in the adult, the formula of the former being I22, C11, P23 [M33], while that of the latter is I22, C10, P22, M33, the lower canine and one lower pre-molar having disappeared. In the upper jaw the incisors are very small, the outer one standing behind the inner one, with a space between the former and the canine; the canines are long, curved behind, and set close up to the anterior pre-molar. The pre-molars are longer than they are broad, laterally compressed, and present to the outside one main triangular cusp with a small accessory cusp on each side, the posterior tooth of the series having a hind inner cusp. The anterior and median molars are four-cusped, of which the outer and inner pairs are separated by a longitudinal groove; to the outside they have one supernumerary cusp on each main cusp, and one between them. The median molar is the largest tooth of the jaw, and the posterior is small, triangular and three-cusped. Of the lower jaw, the outer pair of the long, and almost horizontally protruding incisors, is larger than the inner pair, and is separated by a space from the anterior pre-molar. Of the elongate laterally compressed pre-molars, the anterior is the larger, and is vertically taller than its fellows, being slightly depressed forward and curved behind; the posterior pre-molar has one cusp. The molars have four cusps, of which the inner ones alternate with the outer cusps.

The intestinal canal in the Indrisinæ is very long, the cæcum, or blind diverticulum at the junction of its two portions, being extremely long and large, occupying, indeed, a great part of the abdominal cavity. The main arteries of the fore- and hind-limbs do not break up into a rete mirabile, or series of small parallel vessels, as in many other Lemuroids.

In this group, while the sense of smell is very perfect, that of hearing is less acute than in the other Sub-families; and that of touch conspicuously blunt, both in the fingers and toes, which are chiefly climbing and not tactile and prehensile organs, as they are in the corresponding limbs of the Anthropoids. The female never produces more than one young at a birth.

The convolutions of the brain are few, but they are more complicated than in many of the South American Monkeys. In very young individuals the cerebellum is more covered by the cerebrum than it is in the adult.

The species of this Sub-family are confined to the island of Madagascar. Our knowledge of their general characters, anatomical structure and habits, is very complete, through the researches, both in the field, of M. Grandidier, and in the study, of Prof. Alphonse Milne-Edwards. These results are published in their magnificent "Histoire de Madagascar," to which the reader is referred for fuller information.

The Indrisinæ, on account of their superior organisation, and especially their relatively large brain, are considered to be the highest of all the Lemuroids. They are essentially arboreal. If they come to the ground they sit upright on their hind-legs, and progress by jumps, holding their arms above their heads. They are easily tamed, and become gentle in confinement; but they are not very intelligent. The Endrinas "never manifest in any very marked manner," so MM. Milne-Edwards and Grandidier tell us, "the passions that affect the Apes so vividly; their countenance, almost as immobile as that of an herbivorous or carnivorous animal, exhibits neither anger nor pleasure. In captivity they do not seek to be caressed; they appear neither to become attached to their master, nor to take interest in anything about them." Many of their actions, however, and the peculiar sounds they often utter, recall those of Monkeys.

Some of the species are diurnal and others nocturnal.