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Show 644 MR. W. A. FORBES ON THE UAKARI MONKEYS. [Nov. 30, joined by the collateral sulcus1 (cl), which passes forwards and slightly outwards, so appearing on the external face of the temporal lobe (fig. 9). The temporal lobe has, in addition, a slight impression anterior and internal to this, but is otherwise quite smooth below. The corpus callosum is well developed ; it is nearly 1 inch in total length; the prsecallosal part of the cerebrum is 0*45 inch, the postcallosal 0'9 inch in length. The cerebellum is well developed ; the superior vermis is 0*85 inch in length; with the lateral lobes it is altogether 1*25 inch transversely. The flocculi are large, and the pons Varolii well developed. The medulla has distinct olivary bodies. In the general characters of its brain, as will be thus seen, Brachyurus approaches most nearly the genera Cebus and Pithecia (including Chiropotes), and especially the type found in Cebus apella. With Ateles and Lagothrix it has no close relationship ; and the same may be said as regards Mycetes; it also departs widely in the greater complication and development of the brain from Callithrix, Chrysothrix, and the smaller Cebidae generally. Reviewing the facts already stated as to the structure of Brachyurus rubicundus, it is evident that Brachyurus is a perfectly good genus, more or less intimately related to a number of the larger Cebine forms, but nevertheless characterized by a combination of characters peculiarly its own. A relationship to Mycetes, suggested by its external appearance and the form of the lower jaw, is not borne out by its visceral anatomy, the brain and liver both pronouncing decisively against the idea, besides other peculiarities. With Ateles and Lagothrix it has no particular features in common, but it undoubtedly approaches Cebus in the structure of its brain ; and it is with this genus and Pithecia (including Chirojwtes) that it has probably the nearest affinities. The institution of a genus Ouakaria for the reception of these short-tailed Monkeys by Dr. Gray (P.Z. S. 1849, p. 9) seems to me unnecessary. As he there remarks, the genus Brachyurus, as originally proposed by Spix (Sim. et Yespert. Bras. p. 11), contained two species, B. israelita (1. c. pl. vii.) and B. ouaikory (pl. viii.). The former of these is now generally referred to the genus Pithecia, standing as Pithecia chiropotes (cf. Sclater, P. Z. S. 1871, p. 228). Having examined skulls of all the known species oi Brachyurus, as well as oi Pithecia satanas, which is merely a repre- Prof. Flower says of Mycetes (I. c. p. 337), " the dentate sulcus is continuous with the calcarine." O n the other hand, in Ateles (cf. Huxley, I. c. p. 255, fig. 2) it is superficial and obvious. Broca also figures its existence in Laaothrix (I.e. p. 471, fig. 31). 1 This junction, at least superficially, of the calcarine and collateral sulci I also find exists in Cebus capucinus (cf. also Gratiolet's figure, Atlas, pl. x. fig. 9) and Pithecia. satanas; in Ateles and Nyctipithecus, & c , however, it does not exist, as far as I have seen, nor do I find any allusion to such a condition existing at all in any of the memoirs already quoted on the brain of Primates. |