NERVOUS SYSTEM. 81 



Marsupialia. Olfactory lobes large, for the most part 

 rounded and constricted. Cerebrum not encroaching upon 

 cerebellum, is irregularly lobed and smooth. In Macropus 

 (kangaroo) and some other forms, small lateral appendages 

 lie in fossa upon petrous portion of temporal bone. Corpus 

 callosum rudimentary, and in some genera entirely absent. 

 Optic lobes quadri-partite. Relative size of brain less than 

 in other Mammalia. In Dasyurus (dasyure), it is 1 to 520, in 

 Phascolomys (wombat), 1 to 614, and in Macropus^ 1 to 800. 



Hodentia. Brain Cerebrum generally of a rounded 

 shape, not impinging upon cerebellum, and without convo- 

 lutions. Optic lobes quadripartite; nates larger than testes. 

 Cerebellum of moderate proportions, with well-marked 

 hemispheres. 



Cetacea. Brain large, that of the Balcena (whalebone 

 whale) weighing three pounds four ounces. Cerebrum, 

 nearly covers in the cerebellum, is broader than long; the 

 convolutions are numerous and deep. Olfactory lobes rudi- 

 mental, and were believed to be absent. The hemispheres 

 of cerebellum divided into a number of lobes, six on either 

 side, obtained for the most part by subdivision of the lobules 

 mentioned in human anatomy. Trapezium absent. 



Quadrumana. The brains of all the old world monkeys 

 below the Anthropoids possess the following characteristics 

 when compared to that of man. The breadth of encephalic 

 mass is proportionately greater than the length; the cere- 

 bral hemispheres do not cover the whole of the cerebellum ; 

 the convolutions are smaller and less deep; the sensory gan- 

 glia are of small size; the corpora albicantia are united into 

 one mass; the cerebellum is smaller and Pons Yarolii conse- 

 quently less.* 



* The above resume gives, it is thought, the principal variations seen in 

 the nervous system of Mammalia. 



