380 



HITCHCOCK'S ANATOMY 



pensation is effected by the vitreous humor, which refracts less 

 than the lens. 



696. The Secretion of the Lachrymal Glands —The lach- 

 rymal gland is designed to secrete a saltish fluid known as the 

 Tears. This is of great service in lubricating and keeping 

 moist the surface of the eyeball, so that it may move readily 

 in its socket, and also to keep the cornea from becoming hard 

 and dim. The tears also moisten the back part of the nostrils, 

 and are ultimately poured into the pharynx. The amount of 

 tears which is daily secreted is estimated at four ounces, 

 and it is greatly increased by strong emotions, whether pleas- 

 ant or sorrowful, as it is well known that a person is apt to 

 cry when very sad or very happy. 



697. Service of the Eyelids — Necessity of Constantly 

 Winking — Eyelashes. — The eyelids are of service to keep 

 the light from the eyes when it is too intense, or when it is 

 necessary to exclude it entirely, as during sleep. Another 

 valuable service which they perform is to spread the tears 

 constantly and uniformly over the eyeball. This is the rea- 

 son why we are constantly but unconsciously winking during 

 every few seconds of our waking hours. The eyelashes which 

 line the edges of the lids, prevent the perspiration which is 

 secreted on the lids from entering the eye, and thus irritating 

 it, since by the law of capillary attraction the tears will run 

 towards the free extremity of the hair, where they will accu- 

 mulate to such a size that they drop off. The eyelashes also 

 prevent, in some degree, dust from entering the eye. 



698. Use of the Eyebrows. — The eyebrows perform a 

 similar office to the eyelids, though not so important. The 

 hairs which cover them, like the lashes, convey away the per- 

 spiration from the forehead, and allow it to fall in front of the 

 eye, and not directly upon the ball ; while, by means of the 



696. What is the secretion of the lachrymal gland? What is the use of the tears? 

 What quantity of tears are secreted daily? 697. Of what service are the eyelids? Why 

 do we constantly wink? Of what service are the eyelashes? 698. What service do th& 

 eyebrows perform? 



