i86 



THE GROWTH OF THE BRAIN. 



P.d. 



exactly divide it, the right hemisphere would probably 

 be the heavier. If the occipital end were away from the 

 operator, the reverse result would follow. Until, there- 

 fore, it is reported exactly what method was employed 

 in making the division of the brains, it will not be safe 



to attach any importance to 

 the recorded differences in 

 the weight of the two hemi- 

 spheres. 



Asymmetrical develop- 

 ment may in certain cases 

 be the normal. In one in- 

 stance, at least viz., the 

 cerebellar cortex of the cat 

 an asymmetrical develop- 

 ment is a regular occurrence, 

 and preliminary observations 

 show the same to be true 

 for the sheep. In this divi- 

 sion of the brain the mole- 

 cular layer of the cortex 

 shows an average thickness 

 in the right hemisphere, 

 which is always less than 

 that in the left. 1 Perhaps 



this difference is associated 



FlG. 31. Illustrating the par- .^, Jt . . r . 



tial and complete decussa- with the twisting of the ver- 



tion of the fibres of the third mis to the right side ; and as 



and *ZLg*SZ this asymmetrical position of 



tion in the case of the sixth, the vermis is by no means 



1 1 1., root of the third cranial confined to the cat and 



nerve ; IV., of the fourth ; . 



VI.. of the sixth. sheep, but appears in other 



vertebrates, we may expect 

 to find similar differences existing in them also. 



1 Krohn,y0wr. o Nervous and Mental Disease , 1892. 



