Handbook to the Primates/Lorisinae

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[ 22 ]

THE TYPICAL LEMURS. FAMILY LEMURIDÆ.


Under this family heading are included the whole of the remaining members of the Sub-order. They all possess certain main characters in common; but on account of the presence or [ 23 ]absence of certain subordinate features in some of the groups, the family has been further subdivided into four sub-families. The more important characters which they have in common are the thick woolly fur, the Dog- or Fox-like snout and nostrils—a character obviously distinguishing them from the bulk of the Monkeys, in which the nose forms a subsidiary feature, and is not the main part of the face,—and especially the number and form of their teeth. In the centre of the upper jaw there is always a toothless gap, or diastema, on each side of which the teeth are arranged according to the following formula: I 2/2, C 1/1, P 3/3, M 3/3 = 36. Among the Endrinas, however, the formula is I 2/2, C 1/(1 or 0), P 2/2, M 3/3 = 32 or 30 in number. In the upper jaw the incisors are small and perpendicular; but in the lower, where they are long and narrow, they protrude horizontally in front, and then follow, parallel and close to them, the somewhat thicker canines, the six teeth together forming a comb-like series. The anterior pre-molar is always vertically longer than the others, and assumes the form and function of the canines in other animals.

In some genera (e.g., Propithecus), Milne-Edwards has observed that in the young animal the cerebellum is more overlapped by the cerebrum (or main brain) than it is later in life; and Dr. Major believes that the Lemuridæ are highly specialised members of the Sub-order, developed from ancient types which were not unlike the American Monkeys of the family Cebidæ.

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).



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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.

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 [ 25 ]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.


[ 26 ]

THE POTTOS. GENUS PERODICTICUS.

Perodicticus, Bennett, P. Z. S., 1839, p. 109; Huxley, P. Z. S., 1864, p. 235.

Arctocebus, Gray, P. Z. S., 1863, p. 150; Mivart, P.Z.S., 1864, p. 644.

This genus contains two species, both confined to the West Coast of Africa. The Pottos are slender-bodied animals, with oval heads and blunt Dog-shaped muzzles. Their eyes are large and full, and their external ears erect, with shelf-like lamellæ inside. They have slender and sub-equal limbs. The second digit of the fore-limb is rudimentary and nail-less; it is supported on one wrist-bone, and has two phalanges or finger-bones. The great toe is opposable, and the fourth and fifth digits of both limbs are united together by membrane as far as the first joint. The processes of the vertebræ in the neck and back are long and protruding. The tail is very short.

The pre-maxillæ (which carry the incisor teeth) do not project in front, nor does the bony palate extend farther back than the end of the posterior molar teeth. Of the upper teeth the incisors are equal in size (Fig. 6); the median and posterior pre-molars have on their crowns three cusps, of which the two outer are the larger; the anterior and median molars are cingulate, have four-cusped crowns, and are larger than the pre-molars; the posterior is narrow from before backwards, and its crown presents only two or three cusps. Of the lower teeth, the anterior pre-molar is recurved and larger than the canine, with a ridge on its inner face and a cusped heel behind; the median and posterior ones are shorter than their anterior fellow, each having a strong posterior cusped heel; the anterior and median [ 27 ]molars have their crowns four-cusped and are nearly equal in length; the crown of the posterior molar is 4-5-cusped, and has a ridge joining its anterior heel to its front outer cusp. Transverse and oblique ridges are well marked on the crowns of both the upper and lower cheek-teeth.


I. THE CALABAR POTTO. PERODICTICUS CALABARENSIS.

Perodicticus calabarensis, Smith, Proc. Roy. Phys. Soc., Edinb., 1860, p. 172, figs. 1, 2.

Arctocebus calabarensis, J. E. Gray, P. Z. S., 1863, p. 150; Huxley, P. Z. S., p. 314, pl. 28 (1864).

Nycticebus calabarensis, Schlegel, Mus. Pays Bas, vii., p. 287 (1876).

Fig. 7.

Fig. 7. Hand and Foot of P. calabarensis (after Huxley, P. Z. S., 1864, p. 319).

Characters.—Hair long, wool-like; face, hands, and feet thinly haired. Head 2½ inches long, tapering in front; muzzle prominent and blunt; ears large, pointed, and projecting above the level of the head, with short hairs, two lamellæ inside, and marginal tufts; neck short; hind-limbs slightly larger and [ 28 ]longer than the fore-limbs; hands smaller than the feet; thumb thick, with a tubercle at base; the wrist-bone of the very rudimentary index-finger supporting two rudimentary finger-bones; third finger not parallel to fourth and fifth; the fourth longest (Fig. 7). Great toe with a tubercle at its base, opposable. Tail ¼ inch long, hidden in the fur of the body.

Fur grey at base of hairs, fawn-coloured farther up, and tipped with dark brown, uniform over the body and limbs; face darker; sides of head lighter; line from brow down the nose white. No vibrissæ on face and no eyebrows; chin, throat, inner surface of limbs, and under side of body, greyish-white.

Posterior upper molar nearly equal to posterior pre-molar, with the hind inner cusp of the crown rudimentary. Lower incisors not visible beyond the lip, cingulate; posterior molar five-cusped and relatively larger than in the next species (P. potto). Bony palate with large perforations behind the incisors. Intestines, 40 inches long; cæcum, 2½ inches.

Distribution.—The "Angwantibo," as this species is called, is known only from Old Calabar, on the west coast of Africa.


II. BOSMAN'S POTTO, PERODICTICUS POTTO.

Potto, Bosman, Beschrijving van de Guinese Goudkust, ii., p. 32, fig. 4 (1704).

Nycticebus potto, Geoffr., Ann. Mus., xix., p. 165 (1812); Schlegel, Mus. Pays Bas vii., p. 287 (1876).

Perodicticus geoffroyi, Bennett, P. Z. S., 1830, p. 109.

Perodicticus potto, V. der Hoeven, Tijdschr. v. Natuurl. Gesch., xi., p. 41 (1844); Wagner, in Schreber's Säugeth. Suppl., v., p. 183 (1855).

Stenops potto, Pel, Bijdragen tot de Dierkunde, 1852, p. 41.

Characters.—More common than the Angwantibo and [ 29 ]distinguished from it by its rounder, shorter, and wider head, less produced muzzle, smaller mouth, and eyes farther apart; ears shorter, rounder, and directed more backwards, with one lamella on the inner surface. Hands longer, flat and thin; index-finger not so reduced as in P. calabarensis. Tail very short, little more than an inch long, but visible beyond the fur. Length of body, 8 inches.

Upper pre-molars less canine-like than in the preceding species; posterior upper molar differing in size from and set farther out than the others, short and wide, with the crown elliptical and only two-cusped, the two hind-cusps wanting. Lower incisors more prominent and projecting than in P. calabarensis; crown of posterior lower molar four-cusped.

Adult.—Upper surface rich reddish-brown with a black dorsal stripe widening opposite the shoulders, and fading out towards the tail; under side yellowish or reddish-white. Hair on face shorter and paler, with a dark ring round the eyes.

Young.—Reddish-brown all over, redder on the back of the head and neck, darker on the shoulders; creamy-white, washed with rufous, beneath.

Fur silver-grey at the base of the hairs, with reddish-brown tips in younger, and dark golden-brown in older, individuals.

Distribution.—The Potto is one of the oldest known members of the Lemuroid group, having been described in 1704 by Bosman, who met with it on his voyage to Guinea. It was, however, lost sight of until 1825, when it was rediscovered in Sierra Leone and fully described by Bennett in 1830. It is known also from Gaboon.

Habits.—Both species of Potto are nocturnal and arboreal, and are exceedingly slow in their movements. In catching [ 30 ]insects or flies, which form part of their food, they proceed with extraordinary deliberation, never quickening their movements, and yet rarely, if ever, missing their prey.

Bosman in his description of the Gold Coast of Guinea, gives a woodcut of the Potto, which, he says, is a "Draught of a Creature, by the Negroes called Potto, but known to us by the Name of Sluggard, doubtless from its lazy, sluggish Nature; a whole day being little enough for it to advance ten Steps forward.

"Some Writers affirm, that when this Creature has climbed upon a Tree, he doth not leave it until he hath eaten up not only the Fruit, but the leaves intirely; and then descends fat and in very good case in order to get up into another Tree; but before his slow pace can compass this, he becomes as poor and lean as 'tis possible to imagine: And if the trees be high, or the way anything distant, and he meets with nothing on his journey, he inevitably dies of Hunger, betwixt one tree and the other. Thus 'tis represented by others, but I will not undertake for the Truth of it; though the Negroes are apt to believe something like it.

"This is such a horrible ugly Creature that I don't believe anything besides so very disagreeable is to be found on the whole Earth; the Print is a very lively Description of it: Its Fore-feet are very like Hands, the Head strangely disproportionately large; that from whence this Print was taken was of a pale Mouse colour: but it was then very young, and his Skin yet smooth, but when old, as I saw one at Elmina in the year 1699, 'tis red and covered with a sort of Hair as thick set as Flocks of Wool. I know nothing more of this Animal, than that 'tis impossible to look on him without Horrour, and that he hath nothing very particular but his odious Ugliness."


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THE SLENDER LORIS. GENUS LORIS.

Loris, Geoffr., Mag. Encycl., Ann. 2, i., p. 48 (1796).

Stenops, Illiger, Prodr., p. 73 (1811).

As this genus contains only a solitary species, its characters are necessarily those of the species.


I. THE SLENDER LORIS. LORIS GRACILIS.

Loris gracilis, Geoffr., Magas. Encycl. Ann. 4, i., p. 48 (1796); id. Catal., p. 37, no. 1 (1803); id. Ann. Mus., xix., p. 163 (1812); Is. Geoffr., Cat. Méth. Primates, p. 79 (1851); Blyth, Cat. Mamm. As. Soc., p. 19 (1863); Anderson, Cat. Mamm. Ind. Mus., p. 97 (1881); Blanf., Faun. Brit. Ind. Mamm., p. 47 (1888).

Nycticebus gracilis, Fischer, Syn. Mamm., p. 70 (1829); Schl., Mus. Pays Bas, vii., p. 284 (1876).

Stenops tardigradus, Illiger, Prodr. Syst. Mamm., p. 73 (1811, pt.).

Stenops gracilis, Van der Hoeven, Tijdschr., Nat. Ges., xi., p. 39 (1844); Kelaart, Prod. Fauna Zeyl., p. 9 (1852).

Characters.—A slender-bodied animal covered with close, soft, and woolly fur. Head short and round; eyes very large; nose narrow and much pointed; ears small and haired externally; tips nude. Limbs long, remarkably slender and angularly bent; hands and feet covered with short hair; index-finger with three phalanges and finger-bones.

Skull with eye-sockets closely approximating, in the centre separated only by a thin plate of bone; nasal and premaxillary bones prolonged forward to support the narrow pointed nose; cranium, along its base to end of nasal bones, two inches long, broader across the orbits than behind in front of the articulation of lower jaw; bony palate extending back beyond the [ 32 ]posterior molar tooth. In the upper jaw the incisors are small and equal (Fig. 6); posterior pre-molar similar to, but smaller than the anterior molar; anterior molar with the oblique ridge on crown well developed; crown of posterior molar four-cusped, that of the posterior lower molar five-cusped. Dorsal and lumbar vertebræ together, 23; caudal vertebræ, 6-8.

The alimentary canal is four times the length of the body.

Adult.—Dingy grey above, darker on back, paler on lower back; the hairs tipped with white. Sides of body, outside of fore- and hind-limbs dingy white, with a faint rufous wash on the outside of the hind-limbs. Face and ring round eyes dark greyish-brown; streak along nose white, branching on forehead above the eyes on each side into a broad ring encircling the dark ocular ring; this frontal branch sometimes absent. Under side greyish-white. Hairs of fur greyish-white at base, dark in the middle, and tipped with white. Length, 8 inches.

Young.—More rust-coloured than the adult.

Distribution.—The Slender Loris is common in the lower forests of Ceylon and of Southern India, south of the Godaveri river, as well as in those of the Eastern Ghats.

Habits.—This curious, emaciated-looking, little creature is nocturnal, living entirely in trees. It sleeps during the day rolled up in a ball, with its head between its legs, grasping its perch with its hands. According to Jerdon these animals are occasionally brought in large numbers to the Madras market, their eyes being a favourite remedy of the Tamil doctors for ophthalmic diseases.

In its movements it is slightly more active than the Slow-Loris. Its food consists of succulent leaves, honey, insects, birds' eggs, and small animals.

PLATE III.

Plate III.

THE JAVAN SLOW-LORIS.


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THE SLOW-LORIS. GENUS NYCTICEBUS.

Nycticebus, Geoffr., Ann. du Mus., xix., p. 162 (1812).

Stenops (nec Illiger), Van der Hoeven, Tijdsch. Nat. Ges., xi., p. 39 (1844).

Bradycebus, Cuv. et Geoffr., Mém. Class. Mamm. (1795).

This genus, like the last, is represented by a single species, and its characters, therefore, are detailed below.


I. THE JAVAN SLOW-LORIS. NYCTICEBUS TARDIGRADUS.

Lemur tardigradus, Linn., S. N., i., p. 44 (1766, pt.).

Nycticebus bengalensis, Geoffr., Ann. Mus., xix., p. 164 (1812).

Nycticebus javanicus, Geoffr., t. c. p. 164 (1812); id. Cat. Primates, p. 78 (1851); Schl., Mus. Pays Bas, vii., p. 286 (1876).

Nycticebus tardigradus, Fischer, Syn. Mamm., p. 71, no. 2 (1829); Is. Geoffr., Cat. Méth. Primates, p. 78 (1851); Blyth, Cat. Mam. As. Soc., p. 18 (1863); Schl., Mus. Pays Bas, vii., p. 285 (1876); Anderson, Cat. Mamm. Ind. Mus., p. 94 (1881); Blanf., Faun. Brit. Ind. Mamm., p. 44 (1888).

Stenops tardigradus, Van der Hoeven, Tijdschr. Nat. Ges., xi., p. 39 (1844); Wagner in Schreb., Säug. Suppl., v., p. 151 (1855).

Stenops javanicus, Van der Hoeven, op. cit., p. 40 (1844); Wagner, op. cit., p. 152 (1855).

Nycticebus cinereus, Milne-Edw., Ann. Mus., vii., p. 161 (1867); id. N. Arch. Mus., iii., p. 9, pl. 3 (1867); Anderson, Rep. Zool., Yun-nan, p. 103 (1879); Schl., Mus. Pays Bas, vii., p. 286 (1876).

Lemur menagensis, Nachtrieb, Zool. Anz., xv., p. 147 (1892).

(Plate III.)

Characters.—Body larger and fuller than in Loris, and covered [ 34 ]with close and woolly fur. Head short and round. Eyes large, set close together, and having a gentle expression; face short and flat; muzzle less projecting than in Loris; ears small, rounded, hairy, and nearly buried in the fur; neck short; tail invisible externally. Limbs short; index-finger small, containing three bones; toes remaining spontaneously contracted after death. Top of skull with prominent crests, globular behind; facial bones conspicuously projecting in front; orbits large, their inner margins separated from each other by a narrow flat space. Pre-maxillæ not produced far in front; hind border of bony palate not extending backwards beyond the median molar. Of the upper teeth, the inner incisor larger than the outer, one often absent on each side; canine vertically very long, with a gap between it and the anterior pre-molar; anterior pre-molar elongate, the posterior differing considerably from the anterior molar, and having a short cusped heel behind; posterior molar with a three-cusped crown. Teeth of lower jaw agreeing with those in the diagnosis of the family (suprà, p. 24). Vertebræ in dorsal and lumbar regions together 23 or 24. The long flexor muscle of the thumb, so characteristic of the Anthropoid Apes, is present in Nycticebus. The interlacement of the tendons of the muscles of its foot (according to Huxley and Murie) closely resembles the arrangement in the higher Primates. The long flexor muscle of the toes (flexor longus digitorum) is very large, and has one important origin on the lower end (internal condyle) of the thigh-bone correlated with the powerful grasp of its hind-limbs. The female bears one young at a birth.

Above, ashy-grey, rather paler below; more or less silvery on the back, often rufescent on the rump, with the hairs dark ashy at the roots; dorsal stripe from crown to loins chestnut [ 35 ]brown; circle round the eyes dark brown; a white line down the nose between the eyes; oral patch, including the ears, brown.

The Slow-Loris varies greatly in size and colour in the different regions it inhabits, and its varieties have been recognised by many naturalists as distinct species.

Every shade of colour occurs among specimens from different habitats. The colour varies between rufescent grey, or greyish-rufous, or white (with a brown tinge showing through from below) and silvery grey. The dorsal stripe varies from rufous to dull grey or even black, expanding out, or not, on the crown of the head, arms, and cheeks, bifurcating to the orbital rings and ear-patches, or to one or other only. Sometimes the dorsal stripe and face-markings are wanting altogether. Under side varying from pale rufescent grey to light rufous or dull grey. Length of head and body varying from 12¾ to 16 inches.

"It is an interesting fact," observes St. George Mivart, "that as far as concerns the skull and dentition, the Asiatic Nycticebus far more resembles the African Perodicticus than it does its Oriental neighbour Loris."

Distribution.—The Slow-Loris has a comparatively wide and interrupted range. It is common in the dense mountain forests of Assam and Burma (where it has received the distinctive appellation of N. bengalensis), as well as in Tenasserim and the Malayan Peninsula. It has also been obtained in Siam and Cochin-China, whence it has been described as a distinct species (N. cinereus), from its silvery-grey fur; while it also occurs—somewhat reduced in size—and often (but not invariably) without the upper incisor teeth—in the islands of Sumatra, Java, and Borneo with its surrounding islet groups, [ 36 ]as well as in the Philippine Islands. The form from the last-named localities (figured on Plate III.) has generally been recognised as N. javanicus; but, from a careful examination of the material in the British Museum, it appears to the present writer that the specimens from all these localities merge so insensibly into each other that it is impossible to separate them into distinct species. The Slow-Loris, though occurring on the north-eastern frontier of India, has not yet been discovered in the Himalayas.

Habits.—Like the Slender Loris, the Slow-Loris is arboreal and nocturnal, hardly differing in its food and general habits from the latter. It lives alone or in pairs, and moves about very slowly, with its head curiously drawn up close to its body, with the latter arched and its limbs very angularly disposed. Colonel Tickell, has observed it, however, to raise itself on its hind-legs and throw itself upon an insect. It is generally silent, but can utter a low growl when angry. In captivity it becomes docile, but is never very long-lived. Tickell records that "it never by choice leaves the trees.... It climbs readily and grasps with great tenacity. If placed on the ground, it proceeds, if frightened, in a wavering kind of trot, the limbs placed at right angles. It sleeps rolled up in a ball, its head and hands buried between its thighs, and wakes up in the dusk of the evening to commence its nocturnal rambles." Another observer records: "When he climbs he first lays hold of the branch with one of his hands and then with the other. When he has obtained a firm hold with both hands, he moves one of his hind-paws, and after firmly grasping the branch with it, he moves the other. He never quits his hold with his hind-paws until he has obtained a secure grasp with his hands." The remarkable tenacity of grasp in its feet is largely due to the [ 37 ]automatic action of the flexor muscles of the toes (the digits continuing flexed even after death), and the mere extension of the leg largely contributes to the "effortless suspension of the body" (Murie), as in the Fruit-Bats and other species which hang passively by their hind-limbs. (Huxley.)

Dr. Coghlan, speaking of the Chinese race (N. cinereus), says: "They make a curious chattering noise when angry, and when pleased at night they utter a short though tuneful whistle of one unvaried note; this whistle is thought by Chinese sailors, who take them to sea, to denote the coming of wind.... Their intelligence seems to be much below that of the Monkey.... The Slow-Loris, when newly-born, is about four inches long, and covered with fur; it holds on by its four hands to the mother's fur, and in that attitude sucks the milk from its parent's breast."