320 SPECIAL PHYSIOLOGY. 



understood, by tracing the numerous gradations, both general and particular, 

 which it presents in different animals. 



Vertebrata. 



The Encephalon or entire brain. The only animals in which the entire en- 

 cephalon is absolutely heavier than in man are the very largest cetaceans and 

 pachyderms ; thus, in the whalebone whale its weight is about 5 Ibs., and in 

 the elephant it varies from 8 to 10 Ibs., being heavier than in any other known 

 animal. 



The weight of the encephalon as compared with that of the body diminishes 

 in the Vertebrata generally in the following order and manner. In Mammalia 

 it is as 1 to 186 ; in Birds as 1 to 212 ; in Reptiles as 1 to 1321 ; and in Fishes 

 as 1 to 5668. (Leuret. ) Amongst the Mammalia the encephalon as compared 

 with the body is proportionally smaller in the larger species than in those of 

 less dimensions ; thus in the ox it is as 1 to 860 ; in the elephant as 1 to 500 ; in 

 the horse as 1 to 400 ; in the sheep as 1 to 350 ; in the dog as 1 to 305 ; in the cat 

 as 1 to 156 ; and in the rabbit as 1 to 140 ; in the rat as 1 to 76 ; and in the field 

 mouse as 1 to 31. In all these cases, with the exception of the last, the brain 

 is heavier, relatively to the body, than it is in man, in whom the average propor- 

 tion is as 1 to 36.5. In a few other animals the entire brain is also heavier, 

 relatively to the body, than it is in man ; as in the marmozet monkey, in which 

 the proportion is as 1 to 22, and in certain small singing birds, as the linnet, 

 goldfinch, and canary, in which the proportions vary from 1 to 24 to 1 to 14, 

 whilst in the blue-headed tit, the ratio is even as high as 1 to 12. From these 

 facts it appears that, in comparison with the size of the body, Man has a far 

 larger brain than the Vertebrata, even than the warm-blooded groups ; but 

 there are exceptions in the case of a few small birds, in certain small rodent 

 animals, and in the smallest of the monkey tribe. According to recent obser- 

 vations, however, the entire brain of man is heavier, in comparison with the 

 body, than it is in the anthropoid apes, the proportion in an adult Chimpan- 

 zee being about 1 to 50. These facts, especially those derived from a wide com- 

 parison of the weight of the brain and body, in the different classes of the Verte- 

 brata, show such a correspondence between the relative size of the brain and 

 the amount of intelligence exhibited by those animals, as to justify the general 

 inference that the brain is that part of the organism through which the mani- 

 festations of intelligence take place ; for, with apparent exceptions, too few to 

 influence the general conclusion, these facts demonstrate the large relative 

 preponderance of the brain in man associated with his higher mental endow- 

 ments. In reference to the numerical estimates above given of the ratio be- 

 tween the size of the brain and the weight of the body, it must, however, be 

 remarked that the sensory and motor ganglionic masses at the base of the 

 cerebrum, viz., the optic thalami and corpora striata, are always included in 

 the weights ; and moreover that these parts in the lower Mammalia, and espe- 

 cially the corpora striata in Birds, constitute by far the larger part of the so- 

 called cerebral lobes. Hence the numbers do not show the relative size of the 

 parts supposed to be concerned in the manifestation of intelligence, viz., the 

 cerebral hemispheres, properly so-called. Correct estimates would necessitate 

 the removal and weighing of the parts which really form the hemispheres in 

 the lower Vertebrata. But besides size, other conditions have to be considered, 

 particularly the extent of surface and complexity of structure, the quantity or 

 gray matter, and the number of commissural fibres. 



The same general physiological deduction is justified by a comparison made 

 by SoBmmerring between the transverse diameter of the brain and that of the 

 medulla oblongata, regarded as representing the great root of the various nerves 

 of the body. Thus, in man the width of the cerebrum as compared with the 

 medulla oblongata is as 7 to 1 ; in the orang-outang 6 to 1 ; in monkeys gener- 

 ally 5 and 4 to 1 ; in the cat 2.75 to 1 ; in the rabbit 2.66 to 1 ; in the horse 

 2.625 to 1 ; and in the ox 2.6 to 1. Again, the weight of the entire brain as 

 compared with that of the spinal cord, which in man is about 40 to 1, is, in 

 the mouse, 4 to 1 ; in the pigeon, 3.5 to 1 ; in the newt, .55 to 1 ; and in the 

 lamprey, .013 to 1 ; showing a progressive diminution in the brain as compared 



