IN THE EXTINCT LEMUES OF MADAGASCAE. 



171 



Indris brevicaudatus (fig. 56), the inferior frontal is broken up into an anterior part (the 

 true inferior frontal) and an irregular caudal part, the sulcus " e," which is related to 

 the formation of the lower part of the sulcus centralis in the same manner as the sulcus 

 •'/" is related to its upper part [vide supra). 



Thus occasionally in Propithecus and CMromys and constantly in Perodicticus the 

 furrows in the situations e and y come into line and fuse to form a true sulcus centralis 

 such as we find in Pithecia and the Cebidse [see the figures in my earlier memoir, i]. 



It is interesting to note that in this specimen of Mesopropithecus this disruption of 

 the inferior frontal sulcus has not occurred ; hence the similarity of this brain to that 

 of Lemur is much closer than is usual in the Indrisinse. 



In the form of the olfactory bulbs and the extent of the cerebellar overlap this brain 

 resembles those of the living Indrisinse. 



The Fokm of the Beain in Nesopithecus. 

 It is convenient here to return to the consideration of the cranial casts of 

 Nesoptithecus [Qlobilemur), which I have described in my former memoirs (i, 2, and 3). 

 My reason is that I am now able to discuss with more confidence the significance of 



Text-fig. 60. 

 f. s. irttrapar. 



S- front, inf. 

 s.ficrtt.orlit. 



fiss.Syl. 



s. hataty. 



fiss- rJiirv. s. ternp. siip. 



Diagram of a restoration of the left lateral aspect of the brain of Nesopithecus. Natural size. 



the features of this brain, concerning which I felt the greatest hesitation in expressing 

 an opinion before. The renewed study of the brain in the Lemurs has convinced me 

 of the accuracy of the identification of the furrows of this brain in my former 

 communications, and justifies me in discussing the bearing of the cerebral plan so 

 revealed on the affinities oi Nesopithecus. 



A comparison of the cranial casts of Nesopithecus and Mesqpropithecus on the 

 one hand, and the brains of Propithecus and Indris on the other, makes it abundantly 

 clear that the brain of Nesopithecus conforms to the Indrisine type. The greatly 



VOL. XVIII. — PART II. No. 15. — May, 1908. 2 a 



