66 



A COURSE ON ZOOLOGY. 



FIG. 37. 



and called the ciliary process, are really folds of the 

 choroid. 



The eyelids are formed by folds of the skin, and their 

 movements are controlled by several muscles. They are 

 sustained by a thin cartilage, the tarsal cartilage, and 

 their borders are fringed by the lashes. Little glands 

 contained within the upper eyelid secrete a viscous liquid 

 that aids the lashes in arresting dust. 

 The lachrymal apparatus which supplies the tears is 



composed : 1st, of the lach- 

 rymal gland, situated in the 

 superior and external por- 

 tion of the orbit, and dis- 

 tributing by six or seven 

 ducts its secretion over the 

 internal surface of the up- 

 per eyelid ; 2d, of the nasal 

 duct, placed in the inferior 

 and internal angle of the 

 orbit, and carrying the ex- 

 cess of secretion to the in- 

 terior of the nasal fosses. 



of the Meibomian glands; 3, the As an Optical apparatus the 



cartilage of the lower eyelid, also f unct ions like the pho- 



showing on its border the open- J 



ings of the Meibomian glands; 4,5, tOgrapher's Camera. Pho- 



the lachrymal gland; 6, its ducts; tographers place a Sensitive 



7, the plica semilunaris ; 8, the ca- . 



runcula lachrymalis ; 9, the puncta plate that IS, One that IS 



lachrymalia, opening into the lach- capa bl e of being acted On 



rymal canals; 10, 11, the superior 



and inferior lachrymal canals; 12, by light at the back Ot a 



the lachrymal sac; 13, the nasal box blackened inside, and 



duct, terminating at 14 in the lower , A , , , 



meatusofthenose. called a camera. At the 



front of the box is an aper- 

 ture into which is fitted a tube, called the objective, hold- 



THE APPENDAGES OP THE EYE i, the 



