AND PHYSIOLOGY. 



359 



661. Actual Proportion between Cerebrum and Cere- 

 bellum. — According to Cuvier, the proportion of the cere- 

 bellum to the cerebrum, by weight, in the baboon, is as 

 1:7; in the dog, 1:8; in the sheep, 1:5; and in the horse, 

 1:7. 



662. Spinal Cord. — The essential difference between the 

 spinal cord in man and the lower mammalia, is its greater 

 length, and a narrow canal which runs longitudinally through 

 the middle of it. 



Fig. 331. 



663. Nervous System of Birds. — The brain of birds is 

 characterized by the smallness of the hemispheres, though 

 more fully developed than in 

 reptiles and fishes. In the 

 sparrow the weight of the 

 brain to the whole body is as 

 1 : 25 ; in the goose, 1 : 300 ; 

 and in the cassowary, 1 : 1000. 

 It is destitute of convolutions, 

 or in other words is perfectly 

 smooth on its surface, and has 

 large cavities or ventricles con- 

 taiued in it : and, as in mam- 

 mals, the mass of the brain 

 is greater than that of the 

 spinal cord. The pairs of the cerebral nerves are the same 

 as in mammals ; also the principal divisions are the same. 

 The cerebellum, as in man, exhibits the arbor vitee when cut 

 through vertically. 



664. Nervous System of Reptiles. — The brain of rep- 



Brain of Buzzard. B, Cerebrum. C, 

 Optic Ganglia. D, Cerebellum. $r, Pineal 

 Gland. 



661. What is the proportion between the weight of the cerebrum and cerebellum in 

 some of the lower animals ? 662. What is the essential difference between the spinal cord 

 of man and that of most quadrupeds? 663. How is the brain of birds characterized? 

 Give some of the proportional weights of it compared with that of the whole body t 



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