SENSE OF SIGHT. 



597 



of the eye as well as by its adaptation to the needs of the organism 

 of which it forms a part." 



Appendages of the Eye. Lacrimal Apparatus. To keep 

 the conjunctiva (the mucous membrane covering the anterior seg- 



FIG. 371. Lacrimal and Meibomian glands, the latter viewed from the posterior 

 surface of the eyelids. (The conjunction of the upper lid has been partially dis- 

 sected off, and is raised so as to show the Meibomian glands beneath.) Jf, 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 conjunctiva ; 7, 8, lacrimal 

 gland ; 9, its excretory ducts, with 10, their openings in the conjunctival cul-de-sac; 

 11, conjunctiva (Testut). 



ment of the sclerotic and the cornea and lining the lids) moist and 

 in normal condition is the function of the tears. They are secreted 

 by the lacrimal gland, a compound racemose gland lodged in a 

 depression at the upper and outer portion 

 of the orbit. Its ducts, about seven in 

 number, open on the upper and outer half 

 of the conjunctiva near its reflection over 

 the eyeball. At the edge of the upper 

 and lower eyelids, at their inner ex- 

 tremities, are openings, puncta lacrimalia, 

 into which the tears pass after performing 

 their function. These openings are the 

 beginnings of the canaliculi (Fig. 372), 

 which open into the lacrimal sac, or 

 the dilated upper extremity of the 

 nasal duct, which discharges at the 

 inferior meatus of the nose, the open- 

 ing here being partially closed by a 

 fold of mucous membrane, the valve 

 of Hasner. 



Meibomian Glands. On the posterior surface of the eyelids, 



FIG. 372. 1, Canaliculus ; 

 2, lacrimal sac ; 3, nasal duct ; 

 4, plica semilunaris ; 5, car- 

 uncula lacrimalis. 



