The third sub-family of the Lemuridæ contains the True Lemurs, which are characterised by the possession of a soft, thick, and woolly fur, the head rounded behind, with a specially elongated muzzle. They have small and oval ears, with the exterior aspect covered with long hair, but the inside naked, except round the margin. Their hind-limbs do not show so great a disproportionate length compared to that of the fore-limbs, as in the next sub-family, the Indrisinæ. The ankle-bones (tarsus) are only slightly elongated, and their toes are not united by a membrane. Their long and bushy tail is sometimes longer and sometimes shorter than the body. The females produce one or two, nearly naked, young at a birth, the mammæ being either two or four in number. The skull presents a central ridge on the frontal bone, and its facial portion is much elongated, the inter-orbital space being depressed and wider, and the orbits also directed somewhat outward and less straightforwardly than in several of the genera already noticed. The maxillary bones are generally much reduced, and the incisor teeth carried by them not unfrequently entirely aborted. The teeth in this Sub-family vary in number from 32 to 36, the dental formula being I(0-2)2, C11, P33, M33. The foot is slightly elongated by the lengthening of the naviculare bone of the ankle, the others being short. In the wrist (carpus) the central bone (centrale) may be present or absent; its absence, however, is a character which is met with otherwise only in Man, the Chimpanzees, and the Endrina and some other Lemurs, to be described later on. The cæcum is not markedly developed.
The external coloration of the species of this Sub-family is remarkably variable, the variation being chiefly in the upper portion of the hairs, as their base is generally slate-grey.
The sub-family Lemurinæ embraces four genera: the True Lemurs (Lemur), of which there are now eight recognised species; the Hattock (Mixocebus), with a solitary species; the Gentle-Lemurs (Hapalemur), containing two species, and the Sportive-Lemurs (Lepidolemur), with seven species. Some of the most elegantly coloured species in the Animal Kingdom belong to this group. They are gregarious, and most of them arboreal, though some are not so. They form rather an exception to the general rule among Lemurs, in not being nocturnal. They feed during the morning and evening, emitting loud cries as they move about, and during the heat of the day, they often lie stretched out in the sun; at night they rest with their long tails coiled about them. In their mode of progression they are more quadrupedal than most of the other Lemuroids; they jump, walk, or run on all fours. Their food consists of fruits, birds' eggs, birds and insects. Their infants are carried about close to, and concealed amid, the hair of their mother's breast; when older they cling to her back.
The True Lemurs are all inhabitants of Madagascar and of the adjacent Comoro Islands. They are unknown on the African continent.
THE TRUE LEMURS. GENUS LEMUR.
Prosimia, Brisson, Regn. Anim., p. 220 (1756).
Lemur, Linn., Syst. Nat., i., p. 44 (1766).
Varecia, Gray, P. Z. S., 1863, p. 135.
This genus contains the typical Lemurs, in their most restricted sense. They are characterised by having a very Fox-like head, and an elongate and tapering face, shelving on each side of the nose. A long fringe of hair surrounds their chin and cheeks. They have all large and tufted ears, and large eyes, with superciliary ridges rising higher than the forehead. Their tail is always half as long as the body at least. The fore-limbs are somewhat shorter than the hind-limbs, and both the wrist and ankles are haired. The ankle is not elongated, nor is the great toe as large as in the next family—the Indrisinæ. On the outside of the palm of the hand and under the base of the fingers are situated fleshy pads, giving them greater grasping power. The True Lemurs have only one pair of mammæ, which are situated on the breast.
In the skull the facial region is much elongated, its measurement from the anterior margin of the orbit forward being greater than the longitudinal diameter of the orbit, and the space between the eye-sockets is narrow and depressed. The bony palate is short, extending back only to the posterior end of the median molar. The posterior portion of the ear-capsules (the mastoidal and squamosal regions) is not inflated—a character which separates this genus from Galago. The pre-maxillary bones are large and protrude in front, if the skull be viewed from the side. The angle of the lower jaw is not produced downwards and backwards. In some species a large maxillary sinus projects into the anterior part of the orbit; in some also the foramen rotundum does not coalesce with the sphenoidal fissure (see page [11]), but has a distinct opening. The teeth are of the normal number, namely thirty-six. In the upper jaw the incisors are small, sub-equal, and situated anteriorly to the canines and are not in contact with each other, or with the latter. The canines are very large, tusk-like, and set in an excavated notch on the jaw. All the pre-molars have one main cusp to the outside; the anterior pre-molar, however, has a supplementary minute front cusp, while the median has in addition one large interior cusp; both it and the posterior pre-molars are vertically taller than their anterior fellow. The molars have two inner cusps, and two main outer cusps with a supplementary minute fore cusp, as well as two cusps on the ridge joining the fore and hind outer cusps; the posterior molar—the smallest of the three—is, however, larger than the posterior pre-molar, and has only the front inner cusp and no supplementary external cusp. The lower jaw shows a gap between the canine and the anterior pre-molar. The anterior pre-molar, which is vertically taller than the rest, is edged and cutting, taking the place of a tusk; the anterior and median pre-molars are also separated by a small space; the latter, which is equal in vertical height to the posterior, has an inner cusp and a low cusped heel. The molars have two outer main cusps, of which the front one is more developed than the hind one, and two inner cusps, often with an intermediate cusp between them; the pair of fore and the pair of hind cusps are joined by transverse ridges, and the two outside cusps by a backwardly directed semicircular ridge; the posterior molar is four-cusped.