812 



PHYSIOLOGY. 



the sensations from each are blended into one perception. The 

 movements of the eyeballs are also adapted to bring the image of 

 the object to fall upon identical parts. The law results that if one 

 luminous point simultaneously impresses two identical points, it must 

 be seen as single and not double. The two images are referred to 

 one point in space and they produce in the individual only one 

 impression. 



The muscles concerned in the movements of the eyeball are as 

 follows : 



Fig. 364. Lacrimal and Meibomian Glands, the latter viewed from 

 the posterior surface of the eyelids. The conjunctiva of the upper lid 

 has been partially dissected off, and is raised so as to show the Meibo- 

 mian glands beneath. (RAYMOND, after TESTUT.) 



1, Free border of upper, and 2, free border of lower lid, with openings of the 

 Meibomian glands. 5, Meibomian glands exposed, and 6, as seen through con- 

 junctiva. 7, 8, Lacrimal gland. 9, Its excretory ducts, with 10, their openings 

 in the conjunctival cul-de-sac. 11, Conjunctiva. 



Inward Eectus internus. 



Outward Eectus externus. 



Upward Rectus superior, obliquus inferior. 



Downward Rectus inferior, obliquus superior. 



Inward and upward Rectus internus, rectus superior, obliquus 

 inferior. 



Inward and downward Rectus internus, rectus inferior, 

 obliquus superior. 



Outward and upward Rectus externus, rectus superior, obliquus 

 inferior. 



