MOVEMENTS OF THE BALL 309 



scure the balls and protect them in front. On their free bor- 

 ders are rows of hairs (eye-lashes) curling away from the 

 globe and shading and protecting it from dust. The lids 

 are closed by the orbicular es palp ebr arum and opened by the 

 levatores palpebrarum superiores. In the ordinary closing 

 of the lids only the upper one is moved, but the lower one is 

 raised in forcible contraction of the orbicularis. Interven- 

 tion of the will is not necessary to the action of these mus- 

 cles, though they are striated. Except during fatigue, the 

 eyes are kept open involuntarily, but when the cornea is 

 touched no effort of the will can prevent contraction of the 

 orbicularis palpebrarum. During sleep the globes are 

 rotated upward. 



The Lachrymal Apparatus. This consists of the lachry- 

 mal glands, canal, duct and sac, and the nasal duct. The 

 secretion of the lachrymal gland keeps the cornea and con- 

 junctiva constantly bathed in a thin fluid. It is situated in 

 the orbital cavity at its upper and outer portion. Its secre- 

 tion is discharged upon the conjunctiva by several little 

 ducts. The excess of secretion is carried into the nose 

 through the nasal duct. Near the inner canthus is a small 

 opening in each lid; these openings are the orifices of the 

 lachrymal canals, which canals join at the inner angle of the 

 eye to form the lachrymal sac ; the sac is continued below as 

 the nasal duct, opening into the inferior meatus of the nose. 

 The secretion of tears is much diminished during sleep. The 

 influence of the nervous system on lachrymal secretion is 

 well known. Emotional disturbances operate through the 

 sympathetic to increase the flow. Irritation of the mucous 

 membrane of the nose or eye is followed by a like result. 



Movements of the Ball. The capsule of Tenon, a fibrous 

 membrane outside the sclerotic, holds the ball loosely in 

 place. A small amount of adipose tissue behind the globe is 

 never absent. Movements of the ball are effected through 

 the action of the internal and external recti, the superior 

 and inferior recti, and the superior and inferior oblique; 



