:\l()KPIl()T.OGV OF TlIF, BRAIX 1\ THE .MAMMALIA. S-IO 



Tlie remarks of (icrvais arc of intei'cst only in so far as tlicy call aifcnliou to the 

 presence of an additional arcuate sulcus [/. c. the scpiratiou of tli ; suprasylvian ami 

 the pseudosylvian sulci] without suggestiui;' any solution. 



In my specimen a the lateral sulcus ])cgins ^posteriorly at a point 8 mm. from th(> 

 mesial plane and an equal distance from the posterior margin ; the anterior extremity is 

 11'5 mm. from the mesial plaiu> and 10 mm. from the; anterior extremity of the 

 hemisphere. The sulcus is 23 mm. long. In none of my specimens, nor iu that of 

 Oudemans, csn I find auy trace of a separate postlateral sulcus, hut in the left hemi- 

 sphere of the specimen /3 there is a characteristic mcsially-heut tailpiece such as we 

 have seen representing the joostlateral sulcus in many Lemurs. 



The furrows which are situated in that region of the hemisphere wliicii lies in front of 

 the lateral and suprasylvian sulci are suhject to consideral)le variation. On the lelt 

 hemisphere of the specimen ^3 there is a typical orhital sulcus, and in a more dorsal 

 position a very obliquely placed sulcus, which a comparison Avith otiier Prosimian 

 hrains clearly shows to he the anterior part of the coronal sulcus. On the right 

 hemisphere of the same brain a shallow depression unites these two furrows. On the; 

 left hemisphere of specimen a, they are joined to form a single transversely-placed 

 arcuate furrow ; on the right hemisphere the orbital furrow has disappeared and there is 

 simply a transverse coronal element. In two of the crania (302 and 302 b) to which I 

 have refcri'ed, the two sulci are well developed and united to form figures, one like a 

 crescent, the other like a letter U placed on its side. 



These sulci are exhil)ited in a typical manner in Oudeuiaus's memoir, and the names 

 " presylvian" and " prorean " which he applies to tliem we shall find in the subsequent 

 discussion to be not inappropriate. 



Midway between the sulcus which I have called coronal and the anterior ends of the 

 lateral and suprasylvian sulci respectively, there ai-e two sulci in the left hemisphere of 

 the specimen 3. The upper of these may be compared Avith the sidcus distinguished by the 

 letter /in Lemur, and the lower one with that called c. These two sulci are united by a 

 shallow furrow to form a long transverse " sulcus centralis" (fig. 35). 



On the rityht hemisphere of the same brain (fig. 36) the two furrows r and /are much 

 smaller and are Avidely separated. The sulcus / is joined to the anterior end of the 

 lateral sulcus, and e remains as a short independent furrow widely separated from all 

 the other sulci on the hemisphere. 



On the left hemisphere of the specimen u (fig. 33) the two sulci ^ and /are united at 

 an obtuse angle, and the former has a horizontal ramus, which recalls the fact that it is 

 really the posterior fragment of the coronal sulcus. On the right hemisphere of this 

 brain the horizontal sulcus is independent of the moderately long central one. 



On the right hemisphere of Oudemans's specimen there is a small triradiate sulcus/ 

 (which he calls " coronal "), and a horizontal sulcus exactly like that exhibited by the 

 right hemisphere of my specimen a. This he calls " prorean," i. e. the same name 

 by which he denotes the anterior element which I call " coronal." This is of interest in so 

 far as he gives the same name (" prorean ") to these two widely-separated furrows, which 

 I also regard as two fragments of one sulcus ("coronal"). On thclcft hemisphere of 



SECOND SERIES. — ZOOLOGY, VOL. YIII. ^^ 



