;o8 



SPECIAL SENSES 



and is covered with a layer of cells of flattened epithelium. The scle- 

 rotic portion is thinner, less vascular and has no papillae. It is covered 

 with conical and rounded epithelial cells in two to four layers. Over 

 the cornea the epithelium of the sclerotic portion is continued in deli- 

 cate transparent layers, without a distinct basement-membrane. 



The Lachrymal Apparatus. The eyeball is constantly bathed in a 

 watery liquid, which is secreted by the lachrymal gland, is spread over 

 the globe by the movements of the lids and of the eyeball and is pre- 

 vented, under ordinary conditions, from overflowing upon the cheek by 

 the Meibomian secretion. The excess of this secretion is collected into 

 the lachrymal sac, and is carried into the nose by the nasal duct. The 



lachrymal gland, the 

 lachrymal canals, duct 

 and sac, and the nasal 

 duct constitute the 

 lachrymal apparatus. 



The lachrymal gland 

 is an ovoid flattened 

 gland of the racemose 

 variety, resembling the 

 salivary glands in its 

 general structure. It 

 is about the size of a 

 small almond and is 

 lodged in a shallow 



Fig. 181. Lachrymal and Meibomian glands (Sappey). 

 I, I, internal wall of the orbit; 2, 2, internal portion of the orbicu- 



orifice for the passage of the nasal artery; 5, muscle of Homer ; 



6, 6, posterior surface of the eyelids, with the Meibomian glands ; 



7, 7, 8,8, 9, 9, 10, lachrymal gland and ducts; u, openings of the 

 lachrymal ducts. 



depression in the bones 



laris palpebrarum; 3, 3, attachment of this muscle to the orbit; 4, of the Orbit at its Upper 



and outer portion. It 

 is closely attached to 

 the periosteum by its 

 upper surface and is moulded -below to the convexity of the globe. Its 

 anterior portion is separated from the rest by a well-marked groove, is 

 comparatively thin and adheres to the upper lid. It presents six to 

 eight (usually seven) ducts, which form a row of openings into the con- 

 junctival fold. Five or six of these openings are situated above the 

 outer canthus, and two or three open below. In its minute structure 

 this gland presents no points of special physiological importance as dis- 

 tinguished from the ordinary racemose glands. It receives nervous 

 filaments from the fifth cranial and the sympathetic. 



The channels by which the excess of tears is conducted into the 

 nose begin by two little points situated on the margin of the upper 

 and the lower lid near the inner canthus, called the puncta lacry- 



