There is one anatomical peculiarity of the body which may also be noticed, as it relates to the movements of the animals, and their trotting and galloping on all-fours. The pieces of the back-bone in the neck have processes which project outwards (transverse processes), and in the Mandrill they have a triangular shape, and a ridge exists upon them, which is the representative of a very distinct piece of bone in most of the other Mammalia. Now, this structure appears to have to do with the attachment of a muscle which is also present in the Macaques, and which reaches from these transverse processes to the spine of the blade-bone (scapula), and its duty is probably to draw this bone forward, and to assist the fore limb in progression.[68]
SKULL OF THE MANDRILL.
Most of the peculiar muscular arrangements of the Cynomorpha previously described are repeated in the Mandrill; but it has some which are of much interest. Thus, the great chest muscle (pectoralis major), which reaches in the higher Apes from the front of the chest to the upper arm-bone, is very large in the Mandrill, and is divided into three portions, and the great air sac of the neck projects between them. There are also muscular fibres connected with the back, which assist the animal in pulling back its upper arm, and they give force not only to blows, scratchings, and tearings, but also velocity to the movements of the whole limb in moving along the ground. Strangely enough, there is a curious resemblance between the muscles of the thumb of the Mandrill and of the Orang-utan, two of them being united together, so as to give the thumb seven instead of eight; the tendons of these muscles (the long adductor and the short extensor) remain, however, separate. This is a part of the anatomy which recalls the corresponding structures in the Carnivora, and indicates the restricted amount of movement in the thumb of the lower Apes and Monkeys.
Having a good digestion, the Mandrill has a tolerably large liver, but it is separated into several lobes, or pieces, which are more in number than those of the other genera; but as it is partly insectivorous in its diet, there is no necessity for a very full-sized large intestine, and this is not furnished with the appendix noticed in the man-shaped Apes.
Finally, as regards the skull, it may be said, that that of a large adult Mandrill is the strongest created; so huge are the jaws, face, teeth, and crest-ridges, that one wonders where its brain can be put in life. The true brain-case is indeed small, and is encroached upon inside by the back of the orbits, whence the eye looks out under the “beetle-brows.”
The forehead bone is triangular-looking, and there is no ascending of the forehead, the bone being, as it were, crushed flat, so as to make a triangular space with the brows in front. Ridges exist on the sides of this space, and pass backwards to the occiput, where they meet side crests from the ear-bones. The occiput is stuck up in a singular manner, and the surface of the bone is strongly marked by the muscles which draw the head backwards. Of course the singular part of the skull is the huge ribbed prominence of the upper jaw-bone on the side of the nose, and the great upper canine teeth.
THE DRILL.[69]
Very little is known about the habits of another Baboon which is found on the coast of Guinea, and which is called the Drill. But it has been described, drawn, and stuffed frequently, and has been called Wood Baboon, the Cinereous Baboon, and the Yellow Baboon. The natives evidently confound it with the young Mandrill; and as it is good-tempered when young they capture specimens for European menageries, where they are commonly to be seen. It appears to be a modified Mandrill, like it in temper, and in its disagreeable adult qualities; it has not, however, the grand coloration of the face, although the prominences of the cheek-bones are present.