800 



of the muscular power of the individual to whom a skeleton under comparison has apper- 

 tained. 



The influence of muscular actions in the growth of bone is more strikingly displayed in the 

 change of form which the cranium of the young carnivore or the sternum of the young bird 

 undergoes in the progress to maturity ; not more so, however, than is manifested in the pro- 

 gress of the development of the cranium of the Gorilla itself, which results in a change of 

 character so great as almost to be called a metamorphosis. 



In some of the races of the domestic dog, the tendency to the development of parietal and 

 occipital cristae is lost, and the cranial dome continues smooth and round from one generation 

 of the smaller spaniel, or dwarf pug, e. g. to another ; whilst in the large deer-hound those 

 bony cristse are as strongly developed as in the wolf. Such modifications however are un- 

 accompanied by any change in the connections, that is, in the disposition of the sutures of the 

 cranial bones ; they are due chiefly to arrests of development, to retention of more or less 

 of the characters of immaturity : even 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 particular 

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



No species of animal has been subject to such decisive experiments, continued through so 

 many generations, as to the influence of diiferent degrees of exercise of the muscular system, 

 difference in regard to food, association with Man, and the concomitant stimulus to the de- 

 velopment 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 inter- 

 muscular crests superadded to the cranial parietes. Yet under the extremest mask of variety 

 so superinduced, 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 external 

 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 acknow- 

 ledged modifiable characters, and might be similarly produced ; but not every deviation from 

 the cranial structure 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 depend- 

 ent relation. The Chimpanzees, indeed, differ specifically from both the Orangs and Man in 

 one cranial character, which no difference of diet, habit or muscular exertion can be conceived 

 to affect. 



The great prominent superorbital ridge, for example, is not the consequence or concomitant 

 of muscular development ; there are no muscles attached to it that could have excited its 



