196 HAND-BOOK OF PHYSIOLOGY. 



a start of the whole body or an unpleasant sensation, like that produced 

 by an electric shock, throughout the body, and sometimes a particular 

 feeling in the external ear. Various sounds cause in many people a dis- 

 agreeable feeling in the teeth, or a sensation of cold tickling through the 

 body, and, in some people, intense sounds are said to make the saliva 

 collect. 



SIGHT. 



Eyelids and Lachrymal Apparatus. The eyelids consist of two 

 movable folds of skin, each of which is kept in shape by a thin plate of 

 yellow elastic tissue. Along their free edges are inserted a number of 

 curved hairs (eyelashes), which, when the lids are half closed, serve to 

 protect the eye from dust and other foreign bodies: their tactile sensibil- 

 ity is also very delicate. 



Ciliary muscle 



Ciliary 



Canal of Petit- 

 Cornea 

 Anterior chamber 



Iris- 

 Ciliary process- 

 Ciliary muscle 



FIG. 365. 



On the inner surface of the elastic tissue are disposed a number of 

 small racemose glands (Meibomian), whose ducts open near the free edge 

 of the lid. 



The orbital surface of each lid is lined by a dslicate, highly sensitive 

 mucous membrane (conjunctiva), which is continuous with the skin at 

 the free edge of each lid, and after lining the inner surface of the eyelid 

 is reflected on to the eyeball, being somewhat loosely adherent to the 

 sclerotic coat. The epithelial layer is continued over the cornea at its 

 anterior epithelium. At the inner edge of the eye the conjunctiva 

 becomes continuous with the mucous lining of the lachrymal sac and 

 duct, which again is continuous with the mucous membrane of the in- 

 ferior meatus of the nose. 



