ON THE UAKARI MONKEYS. 119 



ferior, external, and internal aspects, of the natural size, drawn after the 

 organ had been hardened in spirit for a short time. 



The total length of the hemispheres is 2-3 inches, their greatest breadth 

 1*8 inch, whilst the vertical depth is about 1'25 inch. Viewed from 

 above, the hemispheres have a fairly rounded contour, and the cerebellum, 

 does not project beyond their posterior margin, though it appears above 

 in the middle line between the somewhat cut-away inner margins of the 

 occipital lobe. From the side, the hemispheres are seen to be but slightly 

 arched. The occipital lobe is well developed, and the orbital surfaces but 

 little excavated. The temporal lobes are also well developed. 



The hemispheres possess the most important sulci characterizing the 

 Simian brain well developed ; as regards their complexity, they stand 

 between Ateles, Cebus, and Lagothrix, on the one side, and Callithrix, 

 Mycetes, Piihecia, &c., on the other. 



The Sylvian fissue * (s.) is well developed, running upwards and back- 

 wards to end, *3 inch from the middle line of the hemispheres, a little in 

 advance of the spot where the temp oro- occipital sulcus (scissure occipitale 

 externe) first appears externally. It is at first slightly concave forwards, p.z.S. 1880, 

 then convex. At about two thirds of its course it is joined by the well- P- 641 - 

 marked antero-temporal sulcus (ci.t.) (scissure parallele, Gratiolet; premier 

 sillon temporal, Broca), which commences near the lower margin of the 

 temporal lobe. This is a condition not found in Ateles, LagotJirix, Mycetes, 

 or Pithecia monachus ; it is represented by Gratiolet as existing in Cebus 

 capucinus (Mem. Plis. Oer. Atlas, pi. x. figs. 7 & 8), and likewise occurs 

 in Cynocephalus, Macacus, and other Old-world genera. 



Embracing the upper extremity of the Sylvian fissure is a somewhat 

 Y-shaped sulcus, the " stem " of the T being short and springing from 

 the median line, whilst the two arms are much longer and run down- 

 wards and outwards, and in the case of the anterior one forwards as 

 well, on to the external surface of the hemispheres, appearing there one 

 on each side of the upper part of the Sylvian fissure (fig. 9). The 

 posterior of these is, no doubt, the aforesaid temporo-occipital sulcus (t.o.) 

 (scissure perpendiculaire externe of Gratiolet, scissure occipitale externe of 

 Broca). The anterior limb no doubt corresponds to the anterior part of 



* In the following description of the sulci, &c., I have in the main followed the 

 nomenclature proposed by Prof. Huxley in his valuable paper on the brain of Ateles 

 paniscus (P. Z. S. 1861, pp. 247-260, pi. xxix.), and adopted by Prof. Flower in his de- 

 scriptions of the brains of Mycetes seniculus (P. Z. S. 1864, pp. 335-338, pi. xxix.) 

 and Pithecia monachus (P. Z. S. 1862, pp. 328-331). The late Dr. Paul Broca has more 

 recently written an elaborate article on the subject of cerebral nomenclature (" Nomen- 

 clature Cerebrale, denomination des divisions et subdivisions des hemispheres et dee 

 anfractuosites de leur surface," Kevue d'Anthropologie, (2) i. 1878, pp. 193-236). In 

 this he endeavours to limit more strictly than has hitherto been done the terms used 

 by various writers on the structure of the brain, and to introduce a uniform nomen- 

 clature. I have, where necessary, added his names in brackets after those here used. 



