CANADA PORCUPINE 19 



predominating righthanded tendency, many conjectures might 

 be made. Alsberg (2), Baldwin (4), and Mollison (28), along 

 with others, hold that this human trait is due to the fact that 

 people are left brained which is, in turn, attributed to the anat- 

 omical advantage of the left carotid artery over the right, thus 

 giving the left hemisphere more and better blood at a higher 

 pressure. The fact that the habit once formed is scarcely ever 

 broken argues for some advantage which makes it different from 

 most other habits. Baldwin (4) postulates that it must be due 

 to inherited physiological superiority in the quantity, quality 

 or arrangement of the brain material of one hemisphere over 

 the other. The original cause of the differentiation which has 

 resulted in righthandedness he thinks must be due to spon- 

 taneous variation. Livi (27), the distinguished Italian anthro- 

 pometrist, has advanced the theory that righthandedness and 

 lefthandedness ai'e due to "uterine position." He shows that 

 in fully 90% of the cases the left hand and arm of the foetal 

 body are cramped under so as to inhibit prenatal movement 

 while the right arm is above, swings free, and is thus more 

 easily exercised and consequently becomes more fully devel- 

 oped, at the same time most probably inducing greater develop- 

 ment of the hemisphere of the brain in: control. As this is 

 exactly the percentage of righthandedness'among people accord- 

 ing to Buschan (7) it appears a very strong probability. I have 

 nowhere seen the conjecture that the prenatal position may be 

 a result of unsymmetrical development in arm or brain in which 

 case the stronger member would extricate itself and leave the 

 weaker member to sustain the weight of the foetal body thrown 

 OA'er on that side. If this seems to be as reasonable as the other 

 it only serves to remove the problem one stage farther, leaving 

 it still unaccounted for except on the basis of innate physio- 

 logical superiority. Buschan (7) accepts the theory of Livi (27) 

 with a few slight additions, chief among which is the fact that 

 the right breast of the mother is larger and stronger, thus caus- 

 ing the human infant to be held more frequently with its left 

 arm pinioned against the body and its right hand free during 

 a large part of the waking life of earliest infancy, and especially 

 during the feeding period where psycho-motor activity is most 

 intense and steady, or where the greatest rewards of activity 

 are being secured. , -. 



