The brain is relatively large in proportion to the body, and attains in the higher of the two sub-orders its most perfect development. The main brain (or cerebral hemispheres), when viewed from above, in size preponderates over, and conceals (except in the Lemurs) all the other parts of that organ. The surface of its lateral halves, which are connected by transverse bands so as to insure harmony of action between them, is marked by fissures and foldings, or convolutions, which vary in number and complexity, evidently in relation to the intelligence of the animal. The brain within the skull gives origin to the nerves for the chief organs of sense; while from its posterior part it is continued along the back--within a canal formed by the neural arches of the vertebræ--as the spinal column, from which arise the rest of the nerves for the body. The young of all the Primates are nourished in the mother's womb by the passage of material from the blood-vessels of the parent through an organ known as the _placenta_. They are all born in a helpless condition, and remain unable to look after themselves for a considerable period, during which they are dependent on the milk secreted on the ventral surface of the mother by two or four glands, the teats or _mammæ_--those characteristic organs from which the "Mammalia" have derived their name. These glands are present in both sexes, but are functional only in the female. We shall now proceed to describe more minutely the first of the two sub-orders of the Primates--the Lemur-like animals. {8}I. THE LEMURS--SUB-ORDER LEMUROIDEA. The Aye-Aye, the Tarsier, and the True Lemurs constitute this first sub-order. They are characterised by having the muzzle long and narrow, more or less Dog-like in shape, and the upper lip often divided into two by the nose-pad. The external ears (Fig. 1) are enlarged, with flattened margins, but have no "hem" as in the higher Anthropoids. (Fig. 2.) [Illustration: Fig. 1. Lemuroid Ear.] [Illustration: Fig. 2. Anthropoid Ear.] The trunk is relatively long and compressed, and the tail when long is never truly prehensile. Of the limbs, the posterior are longer than the anterior, and all have five digits, each bearing a flat nail except the second toe, which has invariably a long pointed claw, their tips ending in prominent discoidal tactile pads. (Fig. 3.) Of the digits, the index is sometimes quite rudimentary, while the thumb is large, and the great toe especially so, both being opposable. Teats occur on the breast, on the abdomen, or on both.