MOKPHOLOGT OF THE BRAIX IX THE MAMMALIA. 



415 



It is unnecessary to enter any furtlier into tlu^ discussion of the later evolution of 

 this sulcus ill the Apes, Ibrmy views on this subject have been far more aptly expressed 

 than I am capa1)le of stating them, in Ciumingham's monog-raph *. There still remains 

 I'or discussion the most difficult problem in the interpretation of the L'rosiniian sulci, 

 /. e. whether the central (Rolando's) sulcus is r(>prescuted in any form in the Lemurs. 



The central sulcus is easily recognizable in all the Siiniidie and Cercopitlieciche. 

 Nor can there be much uncertainty concerning its identity in tiie larger Celiida". 

 If the smaller Cebidae be studied without comparison with the larger members of the 

 family, it may seem very doubtful whether the small central sulcus in such a form as 

 (lirnsothrix (for example) might not really represent the ramus postcentralis of th«! 

 intraparietal sulcus. But an examination of the brain in tlu; whole Family shows that 

 the postcentral sulcus first appears long after the central itself is fully formed. So that 

 in those Cebida) in which only one sulcus is present in the appropriate place, it may be 

 regarded as the central. 



The simplest form of a well-defined central sulcus may be seen in the geiuis Pithcci(( 

 as a simple transverse sulcus in the interval between the intraparietal and " coronal "' 

 sulci. 



In the genus Calllfhrir there is sometimes no trace of a central sulcus ; in other cases 

 there is merely a shallow depression in front of the intraparietal sulcus, and tiie situation 



% 61, 



P'uhecia. — Dorsal aspect of bniiii. Xat. sizp. 



where one would look i'or the upper end of the central sulcus ; in other cases again there 

 is a small transverse furrow in this situation. 



Beddard represents this sulcus in its best-developed form in the brain of CuUUhrix 

 torquata f, and calls it precentral. 



The hraiu of CoUithriv is of peculiar interest to tlie student of the Prosimian organ, 

 because the arrangement of the sulci on the outer surface of its cerebral hemisphere 

 exactly reproduces that found in the Lemurs, as Sir William Flower forty years ago 



* D. .J. Ciinniiigluim, "Surface Anatomy of the Primato Cerebrum," ' C'uuniugbam Memoirs,' Xo. VIJ. Itoyal 

 Irish Academy, 1892, p. 221. 



t "On certain points in the Anatomy of CciUithrir foi-qi'rdi," Xovitates Zoologio;e, vol. viii. October 19(»1, 

 pi. xi. tig. 5 (dorsal aspect, wrongly labelled " mesial "). 



SECOND SERIES. — ZOOLOGY, VOL. VIII. 00 



