The Typical Lemurs are arranged in the following four sub-divisions: The Pottos and Slow-paced Lemurs (Lorisinæ); the Galagos and Mouse-Lemurs (Galaginæ); the True Lemurs (Lemurinæ); and the Endrinas (Indrisinæ).
THE SLOW-LEMURS. SUB-FAMILY I. LORISINÆ.
This Sub-family has been constituted to receive a small number of Lemurs, which, although occupying limited areas in two widely separated continents—one genus being African and the others Asiatic—present certain characters in common. They are recognised by having soft woolly fur, a triangular head and pointed face, very large and staring eyes, set close together, while their ears are naked along their margin. Their fore- and hind-limbs are nearly equal. In the Asiatic genera the index finger is very small, while in the African it is quite rudimentary and nail-less. In both groups the thumb diverges widely from the other fingers, and the great toe is directed backwards, but the ankle-bones of the foot are not elongated. The tail is either so short as to be quite concealed in the fur, or is less than one-third of the length of the body.
Fig. 6. Front Teeth of Perodicticus, Nycticebus and Loris, after Mivart (P. Z. S., 1864, p. 631).
In the skull the squamosal region with the outer and posterior portion of the ear capsules (the periotic) are inflated. The dental formula of the Slow-Lemurs is the same as given above for the family generally. In the upper jaw, the two incisors are usually equal, but, if unequal, the inner incisor is always the larger (Fig. 6); the vertically long canine, which is separated by a gap from the anterior pre-molar, presents both in front and behind a neck or cingulum, which is cusped behind; the pre-molars are canine-like, and have the cingulum produced behind into a heel (or talon). The anterior of the three is vertically longer than the median, while both the median and posterior have, to the outside, one main cusp with a minute one on each side of it, and two inner cusps; the molars are all cingulate, and have to the outside two main cusps (separated by a minute cusp) and two inner cusps, the outer and inner cusps alternating. Of the anterior and median molars, the two main outside cusps are sub-equal, and are flanked on each side by a minute cusp; the posterior molar is short and wide, and has only one minute cusp in front of its anterior main cusp. Of the lower jaw, the pre-molars are canine-like, the anterior being vertically long and having a posterior heel; the posterior pre-molar, which differs in size from the anterior, presents two main cusps to the outside and one minute cusp in front; the molars, both anterior and median, are four-cusped, with a minute cusp in front, the posterior being five-cusped, while all have their front cusps vertically taller than the hind ones.
Among the Lorisinæ the dorsal and lumbar vertebræ together number from twenty-one to twenty-three. The cæcum, at the junction of the larger and smaller intestine, is long. The main artery of the fore- and hind-limbs breaks up into a rete mirabile of numerous small parallel branches.
The Slow-Lemurs are distributed in the western parts of the African continent, and in the Indian, Malayan and Indo-Chinese portions of the Oriental region. It is a remarkable fact that this group should be confined to one portion of Africa and be entirely absent from Madagascar, the country where the Lemurs form so characteristic a feature in the fauna.
The Lorisinæ embrace three genera, the Pottos (Perodicticus) from the African continent; the Slender Loris (Loris), and the Slow-Loris (Nycticebus), both of which inhabit the Oriental region.
THE POTTOS. GENUS PERODICTICUS.