856 EMBRYOLOGY 



None of the secretions concerned in digestion appear to be produced 

 in utero, and it is also probable that the true biliary salts are not formed 

 at that time ; but the katabolic processes and excretion are then active, 

 and the cholesterin of the meconium is the product of the excretory 

 action of the liver. The relations of cholesterin as a product of katabo- 

 lism have already been very fully discussed, in connection with the bile 

 and with excretion. 



Dextral Preeminence. Most persons use the right arm, leg, eye, 

 etc., in preference to the left ; but exceptionally some use the left instead 

 of the right. Exceptions, however, in regard to the eye, are not infre- 

 quent. There can be no doubt of the fact of a natural dextral pre- 

 eminence, and also that left-handedness is congenital, difficult if not 

 impossible to correct entirely, and not due simply to habit. It would 

 appear that there must be some condition of organization, which pro- 

 duces dextral preeminence in the great majority of persons, and left- 

 handedness, as an exception ; but what this condition is, it is very 

 difficult to determine. An explanation offered by some anatomists is 

 that the right subclavian artery arises nearer the heart than the left, 

 that the right arm is therefore better supplied with arterial blood, 

 develops more fully, and consequently is commonly used in preference 

 to the left ; but exceptional predominance of the left hand can not be 

 explained in this way. 



The most important anatomical and pathological facts bearing on 

 the question under consideration are the following : Boyd has shown 

 that the left side of the brain almost invariably exceeds the right in 

 weight, by about one-eighth of an ounce (3.5 grams). In aphasia the 

 lesion is almost always on the left side of the brain. These facts point 

 to a predominance of the left side of the brain, which presides over the 

 movements of the right side of the body. Again, a few cases of aphasia 

 with left hemiplegia, the lesion being on the right side of the brain, have 

 been reported as occurring in left-handed persons. Ogle gives several 

 such instances, in which the brain-lesion was on the right side. In two 

 left-handed individuals, the brain was examined and compared with the 

 brain of right-handed persons. It was found that the brain was more 

 complex on the left side in the right-handed, and on the right side, in 

 the left-handed. Bastian found the gray matter of the brain ordinarily 

 to be heavier on the left than on the right side. In regard to the cause 

 of the superior development of the left side of the brain, the only ex- 

 planation offered is the fact that the arteries going to the left side usually 

 are larger than those on the right. There are no observations respect- 

 ing the comparative size of the arteries on the two sides in left-handed 

 persons. 



