MOEPHOLOGT OF THE BRAI?f IX THE MAMMALIA. 3.')1 



\vhei"eas on tlie right side of this and two other specimens an irrei^idarity is introduced 

 by the development of a side-brancli. The diagonal sulcvxs seems to he more constant in 

 the genus Propithecus than in any other Lemur. 



In only one case — Propithecus Coquereli (fig. 27) — was its presence doubtful; and, as 

 in that particular instance the lateral branch of the orbital sulcus is unusually long and 

 candally extended, the diagonal sulcus can hardly be regarded as absent even in that 

 case. The other sulci on the outer aspect of the hemisphere exhibit a very interesting 

 and most significant series of variations. 



In the type specimen of Propithecus diadenia (figs. 22, 23, and 21') there are lateral 

 and coronal sulci not unlike those of Lemur fiiUnis, but, in addition, there is a small 

 transverse furrow intercalated between the lateral and coronal sulci, which recalls the 

 ventral extremity of the sulcus termed " central " in Perodicticus. 



The posterior extremities of the lateral sulci on the two hemisjiheres curve mestally, 

 as so often happens in the genus iMmur when a well-defined postlateral sulcus is not 

 present. There can be little doubt that these mesially-curved extremities of the lateral 

 sulci may be explained in the same way, even though two short transverse furrows arc; 

 present in the right hemisphere behind the lateral sulci. In a specimen of Propithecus 

 Verreauxii (fig. 25), and also in the actual brain of Propithecus diadema represented in 



ss.. 



Propitjifcus Veri-t'au.rii. 

 riuu of the sulci on the lateral aspect of the left cerebral hemisphere. Xat. size. 



the 'Histoire de Madagascar,' (2) tome vi. pi. 80. fig. 1, the presence and Jiosition of a 

 definite postlateral sulcus, and the absence of an inwardly-bent tail to the lateral sulcus, 

 clearly complete the demimstration of the identity of these two structures. It is further 

 of interest to note the presence in the actual brain of Propithecus diadema of two 

 small transverse furrows such as we have seen in a cast of the same species : seeing that 

 these furrows exist behind a definite separate postlateral sulcus, they aff'onl a further 

 justification for the statements made in the above diseussion. 



The most instructive features in the brain of Propithecus are tlie varying phases in 

 the group of furrows which we may term " central." 



In the only representative of Propithecus dindeni'i (tigs. 22, 215, ami 21) tluu-e is a 

 snuxU transverse sulcus in the situation corresponding to that occupied by the little 

 furrow /' in Leiuur. On the left hemispliere there is a longer transverse sulcus (c) 



SECOND SEIUE-S. — ZOOLOGY, VOL. VIII. 52 



