THE BRAIN OF APES AND OF MAN 255 



like pieces of bone, which increase in area by addition 

 to their margins, and finally meet each other and grow 

 into one another, forming an irregular notched line of 

 junction, which is called a " suture." The sutures them- 

 selves are often obliterated by bony deposit in mature 

 life. In man the bony plates of the skull are separated 

 by large membranous interspaces at birth — " the fonta- 

 nelles" — and by delay in the junction of the bony pieces 

 the expansion of the brain is permitted. About one- 

 fourth of the cases of idiocy reported upon by medical 

 observers are accompanied by an unusually small size of 

 the brain-case (as small in some cases as 750 units), due 

 to the premature closure of its bony walls at an un- 

 usually early period of growth. It, indeed, seems 

 (though this is a suggestion rather than a demonstrated 

 conclusion) that the increase of the size of the brain in 

 normal men, as compared with apes, and the consequent 

 development of increased mental capacity in man, may 

 be directly set up by a delay in the ossification of the 

 walls of the brain-case in man, as compared with his 

 ape-like progenitors. 



One of the most definite distinctions between present 

 man and the higher apes is the length of time during 

 which the period of growth — namely, " childhood " — and 

 the subsequent adolescent stage of development is pro- 

 longed. The chimpanzee " Sally " was full-grown and 

 adult at eight years of age. Savage races show maturity 

 at an age which seems to Europeans astonishing — some- 

 times as early as the eleventh year. But even within 

 the European area there is great variation in this matter, 

 the Southern people maturing more rapidly than the 

 Northern. There certainly is a tendency in modern 

 civilization to defer the recognition of emergence from 

 childhood, though whether the physical facts of growth 



