1909.] OF MONKEYS OF THE GENUS PITHECIA. 929 



whose observations (9) refer, as it would appear, to the actual 

 specimens upon which the facts described in the other memoirs 

 are based. These authors figure a lateral view of the brain of 

 F. cdhinasa and a mesial section of the brain of P. vionachus. 

 As to jjrevious observations upon the brain of the genus Pithecia, 

 they only mention Flower (5) and Turner (13). 



In the brain of Pithecia pithecia the sulcus rectus was evidently 

 of much the same proportionate size, but each sulcus was a simple 

 obliquely running furrow. There was no branch upon the left- 

 hand furrow (or upon the right), such as is represeiited in all 

 those figures of the brain of P. monaclms to which I have referred 

 above. It is interesting to note that in P. satanas (according to 

 Elliot Smith) it is also the left hemisphere which has a triradiate 

 sulcus rectus. 



The sulcus centralis seems to be exactly as in Pithecia inonachus. 

 Its inner end (some way distant from the mesial edge of the hemi- 

 sphere) is 23 mm. from the anterior end of the hemisphere and 

 25 mm. distant from the hinder end of the hemisphere. It is thus 

 situated very near to the middle point of the bi'ain. These j)i'o- 

 portions appear to agree very closely with those indicated in 

 Dr. Elliot Smith's figure of the brain of Pithecia monachus 

 (11, p. 415, fig. 61). 



There are indications of a precf!?«ira7(« on each side ; these 

 appear to be i-ather fainter than the occasional indications of such 

 a furrow in P. monachus and P. satanas. 



The sulcus lateralis (or intraparietalis) is curved like the letter 

 " S," only in the reverse direction. Its anterior end is situated 

 almost exactly midway between the fissure of Kolando (centralis) 

 and the Sylvian. It is a little more extensive on the left side, 

 where it ends i-ather nearer to the middle interhemispheral 

 sulcus. Posteriorly this sulcus is quite unconnected with the 

 sulcus transverso-occipitalis, as will be seen by an inspection of the 

 accompanying figure (text-fig. 286, p. 930). 



The sulcus parieto-occipitalis appears for some distance upon 

 the dorsal aspect of the brain, and the two furrows i-ight and left 

 have to each other exactly the i-everse relation to that which is 

 shown in the same furrows in Pithecia inonachus by both Flower 

 and Elliot Smith. In the latter the left-hand furrow lies rather 

 in front of the right, while in the brain of P. pithecia examined 

 by myself the right-hand furrow is distinctly in advance of the 

 left. This position of the parieto-occipital fissure is obviously 

 related to the asymmetry shown by the lateral fissure, since in 

 both hemispheres the parieto-occipital exactly divides into two 

 the area of brain partly enclosed by the semicircle formed by the 

 posteriorly situated half of the lateral fissure. 



The Sylvian fissui'e has the same relations to the postsylvian, or 

 jKirallel fissure, that it is repi-esented to have in the specimen of 

 the brain of P. ononachtis figured by Elliot Smith in the " Cata- 

 logue of the Royal College of Surgeons Museum " ; that is to 

 say, the two fissures incline towards one another superiorly though 



