DR DUBOIS ON PITHECANTHROPUS ERECTUS. 89 



general organisation, the superior always has the larger brain. For 

 example the Siamang {Hy/obatcs syndactylus), an anthropoid ape, 

 the Budeng {Seinnopithcciis inaiiriis), a lower ape, the Civet-cat 

 {Viverra civetta), the Javanese Pangolin {MaJiis javanica), have 

 about the same body-weight ; however this is in the Siamang 

 73 times heavier than the brain, in the Budeng 126 times, in the 

 Civet-cat 202 times, in the Pangolin 615 times. The Silky Mar- 

 moset {Midas rosalia) possesses one gramme of brain for every 

 26 grammes of body-weight; but the equally heavy common 

 squirrel one gram of brain for 56 grammes of body-weight. 



Comparing two mammals having an equally organised brain, 

 but who are of very different bulk, the larger one has absolutely 

 the heavier brain. The Lion has seven times as much brain as the 

 Cat, the Brown Rat five times and a half as much as the House- 

 mouse, the brain-weight of the Beisa, a species of Antelope equal in 

 bulk to the Stag, is nearly seven times as large as that of the 

 Pygmy-antelope, a species little bulkier than a Common Hare. 



From these comparisons it is evident, that in every animal the 

 size of the brain depends upon two factors, firstly upon the degree 

 of organic development of the brain, i.e. of the cephalisation of the 

 central nervous system, but secondly also upon the size of the body. 



For the size of the body, however, it is not permissible simply to 

 take the weight of the body. For comparing the body-weight of 

 closely allied mammals, we do not find that the weight of the brain 

 in every group is the same fraction of the weight of the body. 

 Universally we observe that the smaller animals possess higher 

 " relative brain-weights." In the Cat it was observed to be -^ and 

 in a full-grown Lion -^\-^, in the House-mouse -^-^ and in the Brown 

 Rat Y^, in the Pygmy-antelope -^-^ and in the Beisa 3^. The 

 relative brain-weight of man {-^^ to -^ is only exceeded by that of 

 some very small animals, such as the Lesser Shrew {So}'cx pygniaeus) 

 with J3 brain-weight, the Silky Marmoset with ^V. the Javanese 

 Tupaya with -^j, the Whiskered Bat {Vespertilio mystacintis) 

 with ^V. 



Though the influence of body size upon the weight of the brain 

 may thus be a very apparent fact, nevertheless seldom and with 

 little results has an attempt been made to inquire into the nature 

 and extent of that influence. L^ndoubtedly, this was principally due 

 to the circumstance, that in all the older and in many new observa- 

 tions of brain-weight and of body-weight the fact was not sufficiently 

 taken into account, that brain-weight increases very much less with 

 age than body-weight. In man the brain attains about the 9th year 

 nearly the same weight as it has in the full-grown state, while on 

 the contrary the weight of the youth at nine years is only less than 

 the half of that of the full-grown man. The same holds good, as 

 shown by Weber, for all mammals, the brain always reaches the end 

 of its growth much earlier than the other parts of the body. There- 

 fore only full-grown animals are to be compared. 



