464 



HISTOLOGY 



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 tar- 

 seus externus, at the upper border of the tarsus, and a second arcus tarseus 

 near the free margin of the lid (Fig. 469). They extend also into the con- 

 junctiva bulbi, and near the margin of the cornea they pass inward to 

 unite with the anterior ciliary vessels (Fig. 467). 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 conjunctiva 

 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 GLANDS. 



The lachrymal glands are groups of compound tubular glands, and are 

 therefore provided with several excretory ducts. These are lined with a 

 double row of epithelial ceils, the superficial layer being columnar. The 



excretory ducts pass gradu- 

 ally into long intercalated 

 ducts with a low epithelium. 

 These terminate in tubules, 

 surrounded by a membrana 

 propria, and containing two 

 sorts of cells. Certain cells 

 are tall when filled with se- 

 cretion, which occupies the 

 superficial half of the cell; 

 when empty they are shorter. 

 The cells of the other form 

 are low when full of secre- 

 tion, which gathers in a large 



FIG. 470. From A SECTION OF A HUMAN LACHRYMAL GLAND. 

 X 420. 



A, Gland body; a, tubule cut across; a', group of tubules cut 

 obliquely; s, intercalated tubule; s', intercalated tubule 

 in cross section; b, connective tissue. B, cross section 

 of an excretory ^uct; e, two-rowed cylindrical epithe- 

 lium; b, connective tissue. 



round mass, leaving only a 



thin basal layer of protoplasm. Intercellular secretory capillaries and 

 secretory granules have been demonstrated. Between the gland cells and 

 the basement membrane there are occasional flat cells, which are a con- 

 tinuation of the deeper layer of the epithelium of the duct. The blood 

 vessels and nerves are similar to those of the oral glands. 



At the medial angle of either eye there are two lachrymal ducts which 

 have no connection with the lachrymal glands, but serve to convey the 

 secretions which pass across the front of the eye to the lachrymal sacs. 



