( 365 ) 



length of the hemispheres was 38 mm., the height 23 mm. Some of the 

 furrows are less marked than in ('. qiqnt, others more strongly j)rononnced, 

 and occasionally rather different in their arrangement. Tlie Sylvian fissure is 

 rather more extensive than in C. (jiqot. As will be seen from an inspection of 

 the drawing, it reaches rather farther towards the summit of the hemisphere, 

 and, moreover, bends forward and runs for a short distance parallel to a 

 similar oliliquely-rnnning extension of the antero-temjioral fissnre. Concerning 

 the last-named fissure I have no remarks to offer save that it is ajtpareutly 

 precisely like that of Callithrix gigot. The supra-angular fissure is somewhat 

 S-sha]ied and a little more extensive than in the other species of this genns. 

 Anteriorly it bends towards the outer side of the hemisphere, and passes almost 

 parallel to the Sylvian fissure ; posteriorly it is continuous on one side (the right), 

 with a short transverse fissnre, which, however, on the opposite side is independent 

 of it. What are the homologies of these different regions of the supra-angular 

 fissure in this monkey with similarly situated fissures in other genera ? I believe 

 that the so-called supra-angular fissure of Callithrix is a compound structure, and 

 includes not merely the supra-angular of Cebiis and other types, but a portion of the 

 fissure of Rolando anteriorly, and either the Simian fissure or the parieto-occipital 

 posteriorly ; and for the following reasons. I may, first of all, again emjihasise the 

 remarkable likeness which the position and appearance of the supra-angular fissnre 

 bears to the similarly named fissure in the brain of many Lemurs. It has, for 

 instance, the same S-shape in Hapalemur.* This is, of course, duly pointed out by 

 Flower, wiio places side by side figures of the brain of this genus of monkeys and 

 the brains of one or two Lemurs. Now the Lemurs are to be differentiated from the 

 higher ju'imates by the fact that their brains do not exhibit any apparent trace of 

 a fissure of liolando, so constant a feature of all monkeys and apes. In Callithrix 

 a small fissnre, lettered a in the drawing on Plate XL, is considered by Weldon 

 to be the equivalent of this fissure, which he follows Huxley in terming " postero- 

 parietal " — a term, by the way, which aj)pears to be most unsuitable, considering that 

 it lies anteriorly to the parietal region, or at least not at its hinder end. 



In examining a series of brains of New World monkeys, Ateles ater, Mycetes 

 fuscus, Cehus hypolcucm, Brachjurus rubicund us, Lagothrix humboldti, as well as 

 figures of the same and of other brains, I find that the fissure of Holando is situated 

 with great regularity at a point rather more than half the length of the brain from 

 the posterior end of the hemispheres. It nearly, but not quite, marks the middle 

 line of the hemisphere, being situated rather nearer to the anterior end of the brain. 

 Now in Callithrix the sujiposed fissure of Rolando is very much farther forward, as 

 will be obvious from a comparison of my figure with, c.i/., that of Flower f illustrating 

 Pithecia. On the other hand, the anterior end of the supra-angular fissure— that 

 portion of it which is bent round towards the outside of the brain nearly at right 

 angles to the rest — is in an ideal position for a fissure of Rolando. In that case the 

 straighter part of the sujira-augnlar fissure may perhaps be compared to the intra- 

 parietal of higher apes,| which sometimes connects the fissure of Rolando with the 

 l>arieto-occipital or the Simian fissure behind. Moreover, in an example of a brain 

 of Mycetes fuscus which I have in my jmssession, there is no actual union between 

 the supra-angular fissure and an (indisputable fissure of Rolando. In that case we 



• BccUl.ird, " Additional Notes upon Hcqiali'iiiiir grisns " {P.fC.S., 1891, p. 4u7, fig. 4). 

 t In .1 p.iper upon tlic l>rain of Pithi'citi mnnncliiia in P.Z.S., Istj2, p. 33G, 

 I It is so comp.ired tjy ICiikonttial & Ziehen, hir, cit. 



