ARCHITECTURE AT MATURITY. 183 



Table 42 gives the records as taken from Ambialet's 

 paper, and below in each case similar averages derived 

 from the study of normal brains observed by Broca. 

 (French subjects, 70-90 years of age.) 



Changes in the shape of the brain are not, as might 

 at first sight appear, the result of direct pressure, for, 

 under normal conditions, the encephalon is nowhere in 

 immediate contact with the skull, but the influences by 

 which the brain is reduced below the normal size must 

 be those of disturbed nutrition. Even the form of the 

 brain is to some extent independent of pressure. For 

 instance, the gyri develop on the surface of a growing 

 brain, even though the skull has been removed, and 

 when one hemisphere has been taken out of the cranium 

 the other extends to only a slight degree across the 

 middle line. It appears, therefore, that in all these 

 instances it is not the mechanical conditions which are 

 most effective. 



After the general shape, the bilateral symmetry of the 

 central system is the most important feature. The 

 conception is well founded that the plane which divides 

 the body into two symmetrical portions divides the 

 nervous system in the same way, but in neither case is 

 the symmetry perfect. Granting such symmetry to be 

 the typical condition, what is to be said in the case of 

 persons with skulls which are manifestly very far from 

 symmetrically developed ? In part such deviation 

 shown by the outside of the skull may fail to be repre- 

 sented in the cranial cavity, but in general asymmetry 

 without means asymmetry within, and it is to be 

 expected that in such an individual one half of the 

 encephalon would be heavier than the other, and that 

 the influence of this inequality would extend to all the 

 parts with which it was connected. Excluding the cases 

 which have just been mentioned, it may be fairly asked 



