MAY, 1921. BRAIN OF C^ENOLESTES, HERRICK 161 



some uncertainty) at the posterior border of the pons. Immediately 

 below the pons is a broad, flat, transverse band which is probably the 

 trapezoid body and at whose lateral ends are the stumps of the VIII 

 nerves. The facialis root arises from the infero-lateral surface of the 

 trapezoid body; the IX, X and XI nerves arise from the lateral surface 

 of the medulla oblongata; and medially of these are the XII roots. The 

 pyramidal tracts are visible as light colored bands near the mid-ventral 

 line extending downward from the posterior surface of the pons. At the 

 level of the first spinal roots there is a strong cervical flexure. 



General considerations. Comparing the brain as a whole with those 

 of other mammals, it is seen to resemble most closely those of Notoryctes 

 and Perameles. In all three cases the rhinencephalon is enormously 

 developed, the olfactory bulbs and tubercles being very large. The 

 cerebral cortex is nearly smooth and apparently relative to the total 

 size of the brain less extensive than in any other mammals hitherto 

 described. Elliot Smith's figures of Notoryctes ('95) indicate that in this 

 genus the cerebral hemispheres are relatively smaller than in Ccenolestes; 

 his figure of the ventral surface of Perameles ('02, p. 171, fig. 52) suggests 

 that here the hemisphere is relatively as large as in C&nolestes or larger. 

 In absolute dimensions the brain of Notoryctes is about the same size as 

 that of C&nolestes, while that of Perameles is more than three times as 

 long. The simplicity of these brains cannot, therefore, be correlated 

 directly with the size of the animals. In fact, our figure of the ventral 

 view of the brain of C&nolestes resembles more closely Elliot Smith's 

 figure of the ventral surface of the larger Perameles than of the 

 Notoryctes of equal size. Both Notoryctes and Perameles belong to 

 the Polyprotodontia. The larger members of the Diprotodontia, such 

 as the kangaroos, have larger and more highly convoluted brains than 

 any of the Polyprotodontia. The brain of C&nolestes is more simply 

 organized than that of any Australian diprotodont. 



LITERATURE. 



CROSBY, ELIZABETH CAROLINE. 1917. The Forebrain of Alligator mississippiensis. 



Jour. Comp. Neur., Vol. 27, pp. 325-402. 



SMITH, G. ELLIOT. 1894. A Preliminary Communication upon the Cerebral Com- 

 missures of the Mammalia, with special Reference to the Monotremata and 

 Marsupialia. Proc. Linnean Soc. New South Wales, Series 2, Vol. 9, pp. 635-657. 

 1895. The Comparative Anatomy of the Cerebrum of Notoryctes typhlops. 

 Trans. Roy, Soc. South Australia, 1895, pp. 167-193. 



1 899. Further Observations on the Anatomy of the Brain in the Monotremata. 

 Jour. Anat. and Physiol., Vol. 33, pp. 309-342. 



