THE NERVOUS SYSTEM 301 



fold of the outer layer of gray cells of the brain, 

 carrying its supply of blood. This layer is called the 

 cortex. The folds are called Convolutions (see Plate 

 VII). 



558, The Weight of the Brain of the average man is forty- 

 nine ounces (a little over three pounds), and of the average 

 woman is forty-four ounces. The woman's brain is as large 

 in proportion to the size of her body as man's brain. 

 Man's brain is surpassed in weight by the brains of only 

 two animals. A whale, measuring seventy feet long, has 

 a brain weighing only five pounds, and an elephant's enor- 

 mous body is controlled by a brain of about eight pounds. 

 Birds' brains are heavier in proportion to their bodies than 

 the brain of any other animal. The brain grows very 

 rapidly till the fifth year, then very slowly; the growth 

 after twenty is very slight. Cromwell's brain is said to 

 have weighed almost eighty ounces. Other great men 

 have had large brains, but some great minds have inhab- 

 ited very small brains. Quality is as important as quantity. 

 The brains of idiots are usually very small. 



559. The Parts of the Brain are the cerebrum, cerebellum 

 and cerebral ganglia. The cerebrum, or great brain, is 

 highest in the skull, and covers all the other parts ; man 

 is the only animal of which this is true (Plate VI). 

 Sense-perception, consciousness, reason, and the will are 

 located in the cerebrum. 



The cerebellum, or small brain, is at the base of the 

 skull behind. If a pigeon has its cerebellum removed, 

 it is restless and has wide-open eyes ; it flutters, but can- 

 not fly. If the cerebrum is removed, leaving the cere- 

 bellum, it is stupid, but flies if thrown into the air. By 

 placing the hand at the back of the skull between the 

 occiput and the neck, you will cover the part occupied by 

 the cerebellum. Coordination of the muscles is believed 

 to be carried out by the cerebellum. You will to walk 



