The brain of one of these Monkeys weighed 460 grains, or the one-eighteenth part of an entire but emaciated body. The general form is a regular arch, and the cerebellum is covered by the brain proper. Its general form is like that of some of the Cebi, and is less pointed than that of the Old World Apes in front, and less elongated and depressed than those of the lowest Monkeys of the New World, such as the marmosets and Tamarins, for instance. On the outer surface of the brain there are few but deeply-cut and characteristic furrows. The fissure of Sylvius slopes backwards and upwards, but not very far back, and ends abruptly. On the front lobe there is a deeply-marked fissure, running crossways, backwards, and outwards, and bent in the middle. Separated from this by a wide interval is the fissure of Rolando. The external perpendicular fissure so common in the Old World Monkeys is just visible. On the inner surface the sulci are present in a simple form, and the calcarine sulcus is well curved, and prolonged and bifurcated. This is a better organised brain than that of the Howler, and is not unlike that of the Spider Monkey. [Illustration: MONK. (From the _Proceedings of the Zoological Society_.)] The second series of the Sakis, or those with only a short tail, or a stump of three inches in length, are called Brachyures, from this peculiarity. THE SCARLET-FACED, OR WHITE-SKINNED SAKI. THE UAKARI, AND THE BALD-HEADED BRACHYURE, OR SAKI.[104] These are the names of a rare Monkey, which Bates described as follows:--“Early one sunny morning, in the year 1855, I saw in the streets of Ega a number of Indians, carrying on their shoulders down to the port, to be embarked on the Upper Amazon steamer, a large cage, made of strong lianas, some twelve feet in length and five in height, containing a dozen Monkeys of the most grotesque appearance. Their bodies (about eighteen inches in height, exclusive of limbs) were clothed from neck to tail with very long, straight, and shining whitish hair. Their heads were nearly bald, owing to the very short crop of thin grey hairs, and their faces glowed with the most vivid scarlet hue. As a finish to their striking physiognomy, they had bushy whiskers of a sandy colour, meeting under the chin, and reddish-yellow eyes. They sat gravely and silently in a group, and altogether presented a strange spectacle. These red-faced Apes belonged to a species called by the Indians Vikarof, which is peculiar to the Ega district, and they had been obtained with great difficulty in the forests which cover the low lands, near the principal mouth of the Japura, about thirty miles from Ega. It was the first time I had seen this most curious of all the South American Monkeys. I afterwards made a journey to the district inhabited by it, but did not then succeed in obtaining specimens; before leaving the country, however, I acquired two individuals, one of which lived in my house for several weeks.