HUMAN STRUCTURE AND LIFE-ACTIVITIES 515 



surface layers where the nerve-cells are concerned with special 

 organs; for example, there are such centers for muscular 

 movements concerned in speech, for hearing, taste and smell, 

 sight, touch, and voluntary movements of various organs. 

 This discovery of localized centers in the cerebrum is already 

 valuable to surgeons. For instance, if an injury to a brain 

 interferes with any of the functions named above, the sur- 

 geon knows approximately where to look for broken blood- 

 vessels and other injuries. 



The discovery of the centers controlling certain func- 

 tions has no bearing upon the once-popular pseudo-science 

 called phrenology. That pretended to locate certain general 

 mental powers by the contour of the skull. It was utterly 

 unscientific because (1) there is no evidence of such localiza- 

 tion as phrenology claimed, and (2) there is much evidence 

 against the idea that the outer surface of the skull indicates 

 the degree of development of the brain beneath. 



ORGANS OF SPECIAL SENSES 



442. Structure of Eye. Use a hand-mirror and examine 

 your own eyes after reading the next two paragraphs. Refer 

 frequently to Fig. 164. 



The center of the outer coat of the eyeball in front is the 

 transparent cornea, through which one can look into the 

 interior of the eye. All the remainder of the outer coat of the 

 eyeball is hard, white, and opaque (the sclerotic coat). One 

 might imitate the external appearance of an eyeball by paint- 

 ing a glass ball white, excepting a circular spot to represent 

 the transparent cornea. 



Inside the cornea, and of nearly the same size, is the black, 

 gray, or blue part of the eye with a hole in the center. The 

 color pigment is in a sort of thin membrane (called iris), 

 and the hole in the membrane is the pupil. Just back of the 

 pupil is the lens, which is bi-convex, transparent, and elastic, 



