IN MEDICAL SCIENCE 49 



Will, — theoretically the absolute determining power, 

 practically limited in different degrees by the varying 

 organization of races and individuals, annulled or per- 

 verted by different ill-understood organic changes ; — 

 on all these subjects our knowledge is in its infancy, 

 and from the study of some of them the interdict of 

 the Vatican is hardly yet removed. 



I must allude to one or two points in the histolog^y 

 and physiology of the organs of sense. The anterior 

 continuation of the retina beyond the ora serrata has 

 been a subject of much discussion. If H. Miiller 

 and KoUiker can be relied upon, this question is set- 

 tled by recognizing that a layer of cells, continued 

 from the retina, passes over the surface of the zonula 

 Zinnii, but that no proper nervous element is so pro- 

 longed forward. 



I observe that Kolliker calls the true nervous ele- 

 ments of the retina " the layer of gray cerebral sub- 

 stance." In fact, the ganglionic corpuscles of each 

 eye may be considered as constituting a little brain, 

 connected with the masses behind by the commissure, 

 commonly called the optic nerve. We are prepared, 

 therefore, to find these two little brains in the most 

 intimate relations with each other, as we find the 

 cerebral hemispheres. We know that they are di- 

 rectly connected by fibres that arch round through 

 the chiasma. 



I mention these anatomical facts to introduce a 

 physiological observation of my own, first announced 



3 D 



