CENTRAL NERVOUS SYSTEM. 723 



This, as will be seen, gives the largest brain-weights to the western Europeans, 

 but for a proper interpretation of the results there are needed at least the data 

 concerning stature and age of the cases studied, both of which are here lacking. 



"Weight of Spinal Cord. Comparatively few observations are available 

 for the spinal cord : Mies l found that in adults it weighed 24 to 33.3 grams, 

 with an average weight of 26.27 grams : this for the cord deprived of the 

 nerve-roots, but covered by the pia. The variations due to sex and stature 

 have not been determined. It seems probable, however, that the cord, like 

 the brain, will be found lighter in females and in short persons : Mies states 

 that its decrease in old age is proportionately less than that of the brain. 



Bilateral Symmetry as determined by the Balances. The central 

 nervous system in its larger features is bilaterally symmetrical. In detail, 

 however, there are many deviations. The question at once arises whether 

 these variations are normally wide enough to permit us to attach to them a 

 distinct physiological value. While, morphologically, bilateral symmetry is 

 expressed in the arrangement of the central system, common experience and 

 clinical observations show that most persons are physiologically one-sided, and 

 the two sets of facts are apparently out of harmony, provided an anatomical 

 basis is sought for the physiological reactions. The facts bearing on this ques- 

 tion are the following : 



The two cerebral hemispheres in man are found to weigh within a gram of 

 one another in about one-third of the cases recorded (Franceschi). Larger 

 differences, when found, are not distinctly in favor of either hemisphere, accord- 

 ing to the observations of this same author. The results of those observers 

 who have found one side constantly heavier are discordant. 



In individual cases, of course, wide differences between the weight of the two 

 hemispheres may occur, but these are clearly abnormal. 



Asymmetry Otherwise Determined. Other asymmetry has not been 

 detected by the balances. The human cerebellum has not been studied in 

 reference to its bilateral symmetry, but in cats Krohn 2 found the molecular 

 layer thinner on the right side, and the same is true in the case of the sheep. 

 In both these animals the middle lobe (vermis) is, however, asymmetri- 

 cal, being twisted to the right, and it is just possible that the thickness of 

 the molecular layer may be associated with this arrangement. Flechsig's 

 observations on the asymmetry of the pyramidal tracts have already been 

 noted. 



In connection with these anatomical results it is to be noted that the blood- 

 supply to the anterior portions of the left hemisphere is through the left 

 carotid, which appears mechanically fitted to furnish a more direct supply than 

 does the right ; and, bearing in mind the dominant influence of nutritive con- 

 ditions for nervous response, this arrangement may yet prove to be significant. 



The few data which are available on the asymmetry of the central system 

 do not therefore give us a basis sufficient to explain the asymmetry of function. 



1 Neuroloffische Centralblatt, 1893. 



2 Krohn : Journal of Nervous and Mental Disease, 1892. 



