{191}The vertebral column begins to show the S-shaped flexure, characteristic of Man's back-bone; it presents also a human character in the form of its second neck vertebræ, and there are thirteen pairs of ribs, as in Man. The hindmost vertebræ "give the impression of a rudimentary tail." (_Hartmann._) The humerus is nearly equal in length to the fore-arm; the wrist (_carpus_) has only eight bones (the central bone being absent), agreeing, therefore, with the number in Man. All the ridges and grooves seen in the human brain are present in that of the Chimpanzee, but "they are simpler and more symmetrical, and larger in proportion to the brain." (_Huxley._) The cerebellum, and the nerves also, are larger in proportion to the cerebrum than in Man; and certain structures (the _corpora trapezoidea_) which exist in the brains in the lower Mammalia are absent. These prominences, which are situated in that portion of the brain known as the _medulla oblongata_, at the summit of the spinal cord, disappear, as we have seen, in all the genera of higher rank than the _Cebidæ_, one of the lowest families of the _Anthropoidea_. The brain in its convolutions and in many other respects conforms to that of the Orang. This is especially the case in _A. calvus_. The uvula, which is absent in the throat of the Orang, is pendulous in the Chimpanzees, as in Man. Large air-sacs are also present, and the hyoid bone is excavated posteriorly, suggesting the conformation of the same bone in _Alouatta_ (the South American Howlers). The stomach is very similar to that of Man, and so are the digestive and reproductive organs. The round ligament, attaching the head of the thigh-bone into its pelvic socket, is present, and restricts the flexibility of the hind-limb of the Chimpanzees, compared with that of {192}the Orang. Its presence, however, while acting somewhat less favourably in regard to the climbing capacities of these animals, whose habits are less essentially arboreal than the Orangs', beneficially assists them in walking, affording them a firmer support on the ground. In the Chimpanzee there is always a semi-lunar fold (_plica semilunaris_) in the inner corner of the eye, corresponding to the nictitating membrane (or third eyelid) of birds. In some of the Lemuroids it is well developed (_suprà_, vol. i., p. 90), and is large in some races of men. The Chimpanzee is confined to the West African Sub-region, as defined by Dr. Bowdler Sharpe. It is known from Loango, along the banks of the Upper Congo, and Mr. Monteiro (P. Z. S., 1871, p. 544) says it is quite unknown to the south of the Congo; it also occurs throughout the country of the Manyema, in Central Africa, where Livingstone describes it under the name of Soko; and southward as far as 10° south latitude, to Lake Moero. Schweinfurth has recorded it from the Niam-niam country.