DISSECTION OF THE EYE. 87 



the eyelids to the eyeball is known as i\\t fornix con- 

 ju7ictivcs. The portion of the conjunctiva upon the 

 eyeball can be followed forward easily as far as the 

 cornea. Upon the cornea itself it is reduced to a 

 simple layer of stratified epithelial cells firmly adherent 

 to the proper substance of the cornea, and visible only 

 in microscopic sections. 



4. The Membrana Nictitans. The third eyelid or 

 nictitating membrane is very conspicuous in the dog. 

 It is formed by a fold of the conjunctiva strengthened 

 by a lamina of cartilage, and projects from the inner 

 angle of the eye. In the dead animal it may extend 

 over one third or one half of the exposed portion of 

 the eyeball. In the human eye this membrane is re- 

 duced to a comparatively inconspicuous fold, the' plica 

 semilunaris. 



5. The Harderian Gland. This gland lies on the 

 inner face of the nictitating membrane. It is easily 

 exposed by everting the membrane. It is not present 

 in man. 



6. The Puncta Lacrymalia. On the free edge of 

 each eyelid, about 2 mm. or more from the inner 

 canthus of the eye, are the mouths of two small ducts. 

 Each begins as a small opening on the edge of the 

 lid which leads into a short canal. The two canals 

 end in an expanded portion known as the lachrymal 

 sac, from which the nasal dtut is continued downward 

 to open into the lower portion of the nasal cavity. 

 By means of this apparatus the tears which moisten 

 the front of the eyeball are drained off into the nose, 

 and thence into the pharynx. 



7. The Lachrymal Gland. To expose the tear-gland 

 cut through the skin and conjunctiva outward from 

 the outer canthus for a short distance, and then 



