726 



SPECIAL SENSES. 



follicular glands, with a few delicate hairs on its surface. The conjunctiva 

 is continuous with the membrane of the lachrymal ducts, of the puncta lacry- 

 malia and of the Meibomian glands. Beneath the conjunctiva, except in the 

 corneal portion, is a loose, connective tissue. 



The palpebral conjunctiva is reddish, thicker than the ocular portion, fur- 

 rowed, and presents small, isolated papillae near the borders of the lids, which 

 increase in number and size toward the folds. This portion of the membrane 

 presents large, capillary blood-vessels and lymphatics and is covered with a 

 layer of cells of flattened epithelium. The sclerotic portion is thinner, less 

 vascular, and has no papillae. It is covered by conical and rounded epithelial 

 cells, in two to four layers. Over the cornea the epithelium of the sclerotic 

 portion is continued in delicate, transparent layers, without a distinct base- 

 ment-membrane. 



The Lachrymal Apparatus. The eyeball is constantly bathed in a thin, 

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

 globe by the movements of the lids and of the eyeball, and is prevented, 

 under ordinary conditions, from overflowing upon the cheek, by the Meibo- 

 mian secretion. The excess of this fluid 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 

 depression in the bones 

 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 ante- 

 rior portion is separated 

 from the rest by a well 

 marked groove, is com- 

 paratively thin and ad- 

 heres 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 orifices 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 distinguished from the ordinary racemose glands. 



FIG. 261. Lachrymal and Meibomian glands (Sappey). 

 1, 1, internal wall of the orbit ; 2, 2. internal portion of the orbicularis 

 palpebrarum ; 3, 3, attachment of this muscle to the orbit ; 4, 

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



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



7, 7. 8, 8, 9, 9, 10, lachrymal gland and ducts ; 11, openings of the 

 lachrymal ducts. 



