The sixteenth order of Mammals is that of the Quadrumana, comprising the Apes, Monkeys, Baboons, Lemurs, etc, characterised by the following points:

The hallux (innermost toe of the hind-limb) is separated from the other toes, and is opposable to them, so that the hind-feet become prehensile hands. The pollex (innermost toe of the fore-limbs) may be wanting, but when present, it also is usually opposable to the other digits, so that the animal becomes truly quadru-manous, or four-handed.

2 - 2

2 - 2'

and the molars

3 -3

3 - 3'

The incisor teeth generally are with broad and tuberculate crowns. Perfect clavicles are present. The teats are two in number, and (except in Cheiromys) are pectoral in position, and the placenta is discoidal and deciduate. The Quadrumana are divided by Owen into three very natural groups, separated from one another by their anatomical characters and by their geographical distribution as follows:

Section A. Strepsirhina

The members of this section are characterised by the nostrils being curved or twisted, whilst the second digit of the hind-limb has a claw. This section includes the true Lemurs and a number of allied forms. It is chiefly referable to Madagascar as its geographical centre; but it spreads westwards into Africa, and eastwards into the Indian Archipelago.

Section B. Platyrhina

This section includes those Quad-rumana in which the nostrils are placed far apart; the thumbs of the fore-feet are either wanting, or, if present, are not opposable to the other digits; and the tail is generally prehensile. The Platyrhine Monkeys are exclusively confined to South America.

Section C. Catarhina

In this section the nostrils are oblique, and placed close together. The thumb of the fore-limb

Fig. 449.   Green Monkey or Guenon (Cercocebus sabaeus). (After Cuvier.)

Fig. 449. - Green Monkey or Guenon (Cercocebus sabaeus). (After Cuvier.)

(pollex), with one exception, is present, and is always opposable to the other digits. The Catarhine Monkeys are restricted entirely to the Old World, and, with the single exception of a Monkey which inhabits the Rock of Gibraltar, they are exclusively confined to Africa and Asia. It is in the Catarhine section of the Qiiadrumana that we have the highest group of the Monkeys - that, namely, of the Anthropoid or Tail-less Apes.

Strepsirhina.

This section of the Quadrumana, as before said, is characterised by the possession of twisted or curved nostrils, placed at the end of the snout. The incisor teeth are generally much modified, and are in number as a rule; the lower incisors are produced and slanting; the praemolars are and the molars are tuberculate. The second digit of the hind-limb has a claw, and both fore and hind feet have five toes each, all the thumbs being generally opposable. In the true Lemurs, all the digits, except the second toe of the hind-feet, are furnished with nails.

3 - 3

3 - 3

3 - 3

or

2 - 2

3 - 3

2 - 2,

This section is often called that of the Prosimiae, and it includes several families, of which the Aye-ayes, Loris, and true Lemurs are the most important. In many works the Galeo-pithecus is also placed in this section.

Milne-Edwards and Gervais, from an examination of the placentation of the Lemuroids and of their cerebral characters, conclude that the group should be raised to the rank of a distinct order intermediate between the Carnivora and the Quadrumana.

The family of the Aye-ayes (Cheiromydae) includes only a single animal, the Cheiromys Madagascariensis. In appearance the Aye-aye is not very unlike a large Squirrel, having a hairy body and a long bushy tail. There are no canines, and the molars (fig. 450) are separated by a wide interval from the incisors; while there is the additional Rodent-like character that the incisors are ploughshare-shaped, and grow from permanent pulps. The dental formula is:

i

1 - 1

; c

0 - 0

; pm

1 - 1

; m

3 - 3

=

18.

1 - 1

0 - 0

0 - 0

3 - 3

The fore-feet have five toes, armed with strong claws, but the pollex is scarcely opposable to the other digits. The middle finger is about as long as the ring-finger, but only about half as thick, its last two joints being hairless. The hind-feet have also five toes, of which the hallux is opposable, and the second digit is furnished with a long claw; as are all the toes except the hallux, which has a flat nail. As far as is yet known, the Cheiromys is entirely confined to Madagascar.

The family of the Tarsiidae includes only the singular Tarsias spectrum of Borneo, Sumatra, Celebes, and Banca, remarkable for the extraordinary elongation of the hands and feet. It has a long tail, and is arboreal in its habits.

Fig. 450.   Skull of the Aye aye (Cheiromys), viewed laterally and from the front. (After Owen.)

Fig. 450. - Skull of the Aye-aye (Cheiromys), viewed laterally and from the front. (After Owen.)

In the Nycticebidae are the Loris and the Slow Lemurs, in which there is no tail, or but a rudimentary one; the limbs are nearly equal in size; the ears are short and rounded, and the eyes are large, and are placed close together. The species of this family are all of small size, and are exclusively confined to the eastern portion of the Old World, occurring in Java, Ceylon, the southern parts of Asia, and other localities in the same geographical area. They are nocturnal in their habits, living mostly on trees, and feeding upon insects; and from the slowness with which some of them progress, they are sometimes spoken of as "Slow Lemurs." The best-known species are the Slender Loris (Loris or Stenops gracilis) of Ceylon, and the Nycticebus tardigradus of the East Indies. Here also belong the "Potto" (Perodicticus) of Sierra Leone, in which the index-finger is rudimentary, and the Arctocebus of Old Calabar, in which this digit is completely wanting, and the tail is rudimentary.