168 DR. G. ELLIOT SMITH ON THE BRAIN 



assumes a direction oblique or even at right angles to that which the fully developed 

 central sulcus assumes ; in such instances there can be no question of any " homology " 

 Avith the central, even though we are bound to admit that the causal factors which 

 give rise to "f" and the central sulci are tlie same. 



The brain of Lemur jullyi presents an extreme form of this eccentricity. For the 

 sagittally directed sulcus "/" is at right angles to the line of the true central, i. e. to 

 the caudal boundary of the excitable cortex. 



The cerebellum is overlapped by the cerebral hemispheres to about the same extent 

 as (or perhaps even a little more than) in recent Lemurs. 



The Foem of the Bkain in Mesopeopithecus pithecoides. 



In most respects this is a typical Indrisine brain. In fact, if it had been given to me 

 without any information as to its source I should not have hesitated to identify it as 

 the cranial cast of Indris. The fact that the fronto-orbital sulcus differs in position 

 from that of the living Indrisinae in exactly the same way as that of Lemur jullyi 

 diverges from living Lemurs would not necessarily have excluded the possibility of this 

 being the cranial cast of Indris, because it sometimes (though quite exceptionally) 

 happens in Lemur macaco (and in other species) that the sulcus fronto-orbi talis is 

 outside the orbital depression. 



This cast displaces hardly any more sand than is sufficient to fill the cranium of the 

 Lemur macaco the brain of which weighed 26 grammes. In attributing a weight of 

 27 or 28 grammes to this brain we cannot be far wrong. 



The cerebral hemispheres were 56 mm. long, 45 mm. broad, and 30 mm. deep. 

 Flatau and Jacobsohn's drawings * of the brain of Indris brevicaudatus represent a 

 brain 53 mm. long, 43 broad, and 28 mm. deep. Thus the brain oi MesoiJropithecus is 

 of similar shape and very slightly larger than this brain of Indris. 



The fresh brain of a Propithecus coquereli (which died in the Giza Zoological 

 Gardens and was kindly given to me by Captain Stanley Flower) was 51 mm. long, 



45 mm. broad, and 35 mm. deep; and a cranial cast oi Propithecus diadema measured 



46 mm. long, 36 mm. broad, and SO mm. deep. 



Thus the brain of Mesopropithecus more clearly resembles Indris not only in the 

 arrangement of its furrows but also in its size and proportions. The relative flatness 

 of the brain of Indris as compared with Propithecus is found also in Mesopropithecus. 



The furrows on the surface of this cast are deep and have widely separated lips. 

 This deepness and openness of the sulci is also found in the living Indrisinse. The 

 arrangement of the sulci almost exactly reproduces the pattern exhibited in the cranium 



* These are the only figures representing this brain available to me at present. Flatau and Jacobsohn 

 attribute these drawings to Chudzinski ; but I believe their original source is to be found in Grandidier's and 

 Milne-Edward's " Histoire." 



