THE GROWTH OF THE BRAIN. 



weighing from 2 - i6 per cent, (male) to 2*23 per cent 

 (female) of the entire adult body. So long as it is 

 intended to use these figures merely to indicate that the 

 proportional weight of the brain is small, no harm is 

 done, but, given the body-weight, it is quite unjustifiable 

 to attempt to deduce the weight of an individual 

 brain by the aid of it. A moment's thought will 

 show that the chief variable in the original determina- 

 tion of the percentages was the body-weight. The 

 chief variable in this proposed inference is the body- 

 weight, and the variation in that figure being wide, the 

 final result must be correspondingly unreliable. 



Although the problem has been repeatedly attacked, 

 it must be admitted that there is no method of deter- 

 mining with satisfactory accuracy the weight of the 

 brain in the living person, so that for the present at 

 least, the facts obtained by autopsies supplemented by 

 the determination of the capacities of skulls, are alone 

 useful. In studying the questions connected with the 

 weight of the brain it will be necessary to employ 

 descriptive terms which are exact, in order to under- 

 stand just what has been weighed, and a word on these 

 terms is therefore in place. 



The nervous system is divided into a central and 

 a peripheral portion. Since there is no natural line of 

 division between these two, an arbitrary separation is 

 made at the point where the nerves leave the cavity of 

 the skull and vertebral column. Of the -weight and 

 volume of the peripheral nervous system which ramifies 

 through all parts of the body, records are wanting, 

 because of the difficulty in separating it from the sur- 

 rounding parts. But from the cranial cavity and the 

 spinal canal it is comparatively easy to remove the 

 enclosed masses, and thus the brain and spinal cord 

 have been weighed in various ways. To dispose first 



