464 STUDIES IN ADVANCED PHYSIOLOGY. 



occipital lobe arise the fibers for the left half of each retina, 

 while from the left occipital lobe the right half of each re- 

 tina is innervated. This half decussation, of course, occurs 

 in the optic commissure. The destruction of one of the 

 occipital lobes, therefore, produces blindness in the oppo- 

 site half of each eye. 



4. The Auditory Center. Immediately below the fis- 

 sure of Sylvius, in the upper convolution of each temporal 

 lobe is located the center of hearing. Here are stored 

 away the memories of the meanings of all heard words and 

 sounds. Some investigators give the center for perception 

 of musical sounds as somewhat forward from the place where 

 ordinary sounded words are stored. 



5. The Centers for Taste, Smell and Speech. Below 

 the auditory centers in the temporal lobes seem to be located 

 the centers for taste and smell. One of the most interest- 

 ing of all of the centers, and strange, too, one of the first 

 to be localized, is the center of speech. This lies in the 

 left frontal lobe immediately anterior to the motor areas 

 governing lips, pharynx and mouth. The fact that this 

 center is usually located on the left side is explained by the 

 circumstance probably that most persons write with their 

 right-hand, which is a 'form of speaking as far as the intel- 

 lectual part of it is concerned. Persons who have habitu- 

 ally written with their left-hands would be more liable to 

 have the center of speech located on the right side. The 

 interesting question arises, why such a center should be on 

 the one side only? There is no satisfactory reason for this, 

 unless it be that as speech is such a unit, and as its coher- 

 ency would require such a careful co-ordination of two sides, 

 it would hardly be probable that such could be accomplished 

 from the action of two separate centers. .There is the possi- 

 bility of directing the two eyes to two different objects, as 

 in the case of cross-eyed persons, and the ability thus to 

 see, to some extent at least, double. Similar double sen- 

 sations are possible with the ear. Double motions from the 



