380 COMPARATIVE ZOOLOGY 



the organ of sensation and voluntary motion ; the spinal 

 cord is the organ of involuntary life and motion. The 

 brain, above the medulla oblongata, may be removed, 

 and yet the animal, though it cannot feel, will live for a 

 time, showing that it is not absolutely essential to life ; 

 in fact, the brain does nothing in apoplexy and deep 

 sleep. All of the cord, except that part containing the 

 centers for respiration and circulation, may also be 

 destroyed, without causing immediate death. 



The Brain is that part of the nervous system con- 

 tained in the skull. 139 It increases in size and com- 

 plexity as we pass from the fishes, by the amphibians, 

 reptiles, and birds, to mammals. Thus the body of the 

 cod is 5000 times heavier than its brain in fact, the 

 brain weighs less than the spinal cord ; while in man, 

 the brain, compared with the body, is as I to 36, and is 

 40 times heavier than the spinal cord. The brains of 

 the cat weigh only i oz. ; of the dog, 6 oz. 5^ dr. ; and 

 of the horse, 22 oz. 15 dr. The only animals whose 

 brains outweigh man's are the elephant and whale 

 the maximum weight of the elephant's being 10 Ibs., 

 and of the whale's 5 Ibs. ; while the human does not 

 exceed 4 Ibs. Yet the human brain is heavier in pro- 

 portion to the body. But quality must be considered 

 as well as quantity, else the donkey will outrank the 

 horse, and the canary bird, man ; for their brains are 

 relatively heavier. 



The main parts of the brain are the cerebrum, cerebel- 

 lum, and medulla oblongata. 



The cerebrum is a mass of white fibrous matter cov- 

 ered by a layer of gray cellular matter. In the lower 

 vertebrates, the exterior is smooth ; but in most of the 

 mammals it is convoluted, or folded, to increase the 

 amount of the gray surface. The convolutions multiply 

 and deepen as we ascend the scale of size and intelli- 



