The Nervous System. 109 



inflammation material may be deposited, such is often 

 thought by people ignorant of the construction of the 

 cornea to be a scum; it is important to remember that 

 this is not the case and that therefore the use of strong 

 irritants such as powdered alum or powdered glass is not 

 only cruel but wrong and never beneficial. The eyelids 

 are two movable curtains having in their free edges hairs 

 (eyelashes) and glands. The eyelashes are to prevent 

 the entrance of particles of dirt, the gland's secretion 

 retains the tears, in sick animals the secretion of these 

 glands is seen at the inner corner of the eyes as a sticky 

 matter. 



The haw, or rnembrana nictitans is placed at the inner 

 corner of the eye, it is somewhat gristly in its nature 

 and has the important function of removing dirt from 

 the eye. Its development depends on the use of other 

 members of the body to remove dirt, etc., e. g., in cat- 

 tle it is quite large, whereas in man and monkeys it is 

 very small, the latter being able to remove- foreign matter 

 by their hands; its functions being known, none but ig- 

 norant persons will remove it unless diseased. In lock- 

 jaw (tetanus) it may be seen to be rapidly passed over 

 the eye, if the head is raised or the animal excited, in 

 such cases it aids in the detection of this serious trouble. 



The tear machinery consists of (1) a gland which se- 

 cretes the tears, situated at the upper part of the eye, 

 (2) a little round reddish brown body in the inner cor- 

 ner of the eye, which directs the tears to (3) the ducts, 

 which carry those tears to the nasal cavity (q. v. ). 

 Tears in animals are for the purpose of moistening the 

 eye ball and to wash off small particles of dirt, it is 



