100 



the large proportional size of the brain in the smaller varieties of 

 house-dog is in a great degree due to the rapid acquisition by the 

 cerebral organ of its specific size, agreeably with the general law 

 of its development, but which is attended in the varieties cited by 

 an arrest of the general growth of the body, as well as of the particu- 

 lar developments of the skull in relation to the muscles of the jaws. 



No species of animal has been subject to such decisive experi- 

 ments, continued through so many generations, as to the influence 

 of different degrees of exercise of the muscular system, difference 

 in regard to food, association with man, and the concomitant stimu- 

 lus to the development of intelligence, as the dog ; and no domestic 

 animal manifests so great a range of variety in regard to general 

 size, to the colour and character of the hair, and to the form of the 

 head, as it is affected by different proportions of the cranium and 

 face, and by the intermuscular crests superadded to the cranial 

 parietes. Yet, under the extremest mask of variety so superin- 

 duced, the naturalist detects in the dental formula and in the 

 construction of the cranium the unmistakeable generic and specific 

 characters of the Canis familiar is. 



This and every other analogy applicable to the present question 

 justifies the conclusion that the range of variety allotted to the 

 gorilla, chimpanzee, and orang-utan, under the operation of ex- 

 ternal circumstances favourable to their higher development, would 

 be restricted to differences of size, of colour, and other characters of 

 the hair, and of the shape of the head, in so far as this is influenced 

 by the arrest of general growth after the acquisition by the brain of 

 its mature proportions, and by the development, or otherwise, of 

 processes, crests, and ridges for the attachment of muscles. The 

 most striking deviations from the form of the human cranium which 

 that part presents in the great orangs and chimpanzees result from 

 the latter acknowledged modifiable characters, and might be simi- 

 larly produced; but not every deviation from the cranial struc- 

 ture of man, nor any of the important ones upon which the 

 naturalist relies for the determination of the genera Troglodytes 

 and Pithecus, have such an origin or dependent relation. The 

 gorilla, indeed, differs specifically from both the orang and man 

 in one cranial character, which no difference of diet, habit, or 

 muscular exertion can be conceived to affect. 



The prominent superorbital ridge, for example, is not the con- 

 sequence or concomitant of muscular development; there are no 

 muscles attached to it that could have excited its growth. It is a 



