HABITS.--Nothing is known of the habits of this rare species, which is the smallest of the Guenons. THE GUEREZAS AND LANGURS.--SUB-FAMILY SEMNOPITHECINÆ. The members of this Sub-family are characterised, externally, by having elongated slender bodies, with their hind pair of limbs longer than their front pair, and a very long tail. {84}Internally their digestive organs differ from those of the _Cercopithecinæ_, the stomach being three times as large as that organ in any Guenon of the same size. Instead of being a simple rounded sac, it is elongate and composed of several pouches. These compartments are quite different, however, from those seen in a Ruminant's stomach, such as that of the Ox. In the latter, each of the various divisions is differently constructed, and its mucous membrane is peculiarly modified; in the Guenon it is divided into two portions, the left of which forms a very considerable cavity, while the right is long and narrow. Two great, strong, muscular bands run along its entire length, one along the greater, the other along the lesser, curvature, like the muscles of the great intestine, forming a series of large cells. (_Otto._) In addition to this, the whole organ is twisted upon itself, so that the entrance and exit regions come to be close together. Its mucous membrane is throughout of the same character and form. The cæcum has no _appendix vermiformis_, or worm-shaped tube, which is the representative (as in Man) of the elongate cæcum found among the Lemuroids, as among most of the Mammals. The muzzle in this Sub-family is very short, and the nose is generally, but slightly, prominent. There are ischial callosities, but no cheek-pouches among the Langurs, though small ones have been described in certain of the Guerezas (_Colobus_). When laryngeal sacs are present they are formed of a single sac with a median aperture into the windpipe, in the space below its superior opening; it may have large prolongations down the front of the neck, as far indeed as the arm-pits. The frontal region of the skull is rounded, and the facial angle is comparatively large. The ascending portion of the hinder part of each half of the lower jaw is high, and its {85}hindmost molar on each side has five cusps to its crown. Their breast-bone is very narrow. The vertebræ forming the tail are much elongated. All have the central (_os centrale_) bone in the _carpus_ (or wrist). The posterior lobes of the cerebrum project beyond the cerebellum and conceal it; they are very short among the Langurs. The principal grooves and foldings seen in the human brain are represented, and there is a perfectly distinct _hippocampus minor_--an eminence in the cavity of the posterior lobe, which was for a long time supposed to be a character peculiar to the human brain, and the presence or absence of which was once a celebrated cause of difference between certain distinguished anatomists.