LACHRYMAL GLANDS. 377 



occur at the posterior edge of the lid or quite high on the conjunctival sur- 

 face. Toward where the palpebral conjunctiva arches to form that of the 

 bulb, its epithelium is so folded that in sections it may seem to form glands. 



The conjunctiva bulbi is similar to that of the lid. Its outer epithelial 

 cells, however, become squamous toward the cornea and over the exposed 

 portion of the eye. Its basal cells contain pigment, except in the European 

 races. The yellow color, often most pronounced near the medial border 

 of the cornea and known as pinguecula, is said not to be due to fat or to an 

 epithelial pigment; it accompanies a thickening of the connective tissue 

 layer. The tunica propria forms well marked papillae near the cornea. 

 Its lymphocytes may form nodules, as many as twenty having been found 

 in the human conjunctiva bulbi. Occasional mucous glands occur. (It 

 may be noted that the entire anterior covering of the bulb of the eye is 

 named by some the conjunctiva bnlbi, which accordingly is divided into the 

 con], sclerae and the con], corneae.*) 



At the medial angle of the lids there is a thin fold of connective tissue 

 covered with stratified epithelium; this plica semihmaris is a rudimentary 

 third lid. The nodular elevation of tissue at the medial angle, the carun- 

 cula lacrimalis, resembles skin except that a stratum corneum is lacking; 

 it contains fine hairs, sebaceous and accessory lachrymal glands, and in its 

 middle part small sweat glands. 



The blood vessels of the lids proceed from branches approaching the 

 lateral and medial angles of the eye. They form an arch, the arcus lar- 

 seus externus, at the upper border of the tarsus (Fig. 427). They extend 

 into the conjunctiva bulbi, and near the margin of the cornea they pass 

 inward to unite with the anterior ciliary vessels (Fig. 425). The lymphatic 

 vessels form a close network beneath the palpebral conjunctiva and a loose 

 one in front of the tarsus. Whether the lymphatic vessels of the conjunc- 

 tiva bulbi end blindly toward the cornea or connect with the canaliculi, has 

 not been determined. The nerves form a very thick plexus in the tarsus 

 and supply the tarsal glands. There are free endings in the conjunctival 

 epithelium, and bulbous corpuscles in the connective tissue beneath. 



LACHRYMAL GLAXDS. 



The lachrymal glands are compound tubular glands with several 

 excretory ducts. These are lined with a double row of epithelial cells, the 

 superficial layer being columnar. The excretory ducts pass gradually 

 into long intercalated ducts with a low epithelium. These terminate in 

 tubules presenting two forms of cells and surrounded by a membrana 

 propria. The cells of one form are tall when filled with secretion, which 

 occupies the superficial half of the eell; when empty they are shorter. 



