122 ONTHEUAKARI MONKEYS. 



sigmoid curve extending very nearly to the middle line. Anterior to this 



is the superofrontal sulcus (s.f.), also curved, though roughly parallel 



with the external border of the hemispheres. The orbital surface of the 



hemispheres is also marked by a somewhat H-shaped complex sulcus 



(indsure en-H.). The occipital lobe is almost entirely smooth ; below a 



sulcus is observable, curving upwards, and ending in a bifurcate manner 



in front of the lower termination of the occipito-temporal sulcus. Pos- 



P.Z. S. 3880 teri 01 to tn i s * 8 a ver J mu ch smaller, short sulcus, easily seen internally, 



p. 642. but only just appearing on the inferior margin of the lobe externally. 



The internal surface of the hemispheres has the ordinary sulci well 

 displayed. The calloso-marginal sulcus (c.m) (scissure sous-frontale), 

 somewhat broken up anteriorly, inclines posteriorly towards the margin 

 P.Z. S. 1880, of the hemispheres, but does not reach it by about *1 inch. The oceipito- 

 p. 643. parietal fissure (o.p) (scissure perpendiculcdre interne) is distinct, inclined 

 first backwards, and then abruptly bent forwards for a small distance. 

 Between its termination and the posterior end of the corpus callosum is 

 a faintly impressed triradiate mark. The calcarine sulcus (c) is well de- 

 veloped, and terminates posteriorly by its characteristic fork ; the point 

 of division is *15 inch from the margin of the brain ; and the upper arm 

 is slightly longer than the lower. The sulcus is continued forwards with 

 an upward concavity to the end of the corpus callosum, where it passes 

 into the dentate sulcus *. At a point *3 inch in front of its bifurcation 

 P. Z. S. 1 880, it is joined by the collateral sulcus t (cZ), which passes forwards and 

 p. 644. 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 



* According to Broca (Revue d'Anthrop. viii.p. 470, 1878) the bridging convolution 

 between the callosal and uncinate convolutions, which here interrupts the apparent 

 continuation of the calcarine into the dentate sulcus, is nearly always present in Mon- 

 keys, although it may be deep and in some cases extremely delicate also. He considers, 

 however, that it is wanting in the Hapalidse. It is certainly present in Sracht/urus, 

 though small and deep. Prof. Flower says of Mycetes (I. c. p. 337), " the dentate 

 sulcus is continuous with the calcarine." On the other hand, in Ateles (cf. Huxley, I. c. 

 p. 255, fig. 2) it is superficial and obvious. Broca also figures its existence in Lago- 

 thrix (I. c. p. 471, fig. 31). 



t This junction, at least superficially, of the calcarine and collateral sulci I also find 

 exists in Cebus capucinus (cf. also Gratiolet's figure, Atlas, pi. 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. 



