360 NORMAL HISTOLOGY. 



The palpebral conjunctiva lines the ocular surface of the eyelids. 

 Since the latter are developed as integumentary folds, at first the conjunctiva 

 resembles the skin, but after the temporary closure of the lids, from the 

 middle of the third month until shortly before birth, it loses its original 

 character, and later, bathed continuously with the secretion of the tear-gland, 

 assumes the general appearance of a mucous membrane. Over the tarsi the 

 palpebral conjunctiva is so tightly adherent to the underlying fibrous plate, 

 that the tunica propria is reduced to an insignificant layer and the Meibomian 

 glands shimmer through the smooth translucent conjunctiva and appear as 

 parallel stripes. On gaining the convex border of the tarsal plates, the 

 conjunctiva becomes loose and movable since the tunica propria, which here 

 connects the epithelium with the underlying fascial tissue, is plentiful. The 

 small tubules, glands of Henle y occupy the subepithelial tissue of this part of 

 the conjunctiva. In the fornix and its vicinity minute lymph-nodules occur, 

 either discrete or in small groups. In the same locality and at the convex 

 borders of the tarsi, small nests of tubular alveoli, known as accessory tear- 

 glands, or glands of Krause, are found. They are much more numerous 

 in the upper than in the lower lid. 



The bulbar conjunctiva passes from the fornix onto the anterior part 

 of the eyeball, over which it extends as far as the corneal margin, at which 

 point (limbus cornets) the tunica propria ends and the epithelium alone con- 

 tinues uninterruptedly over the cornea. During its passage from the free 

 edge of the eyelid to the cornea, the character of the conjunctival epithelium 

 varies in different parts of the sac. Thus, at the border of the lids and for 

 a few millimeters over the tarsi, it resembles the epidermis in being stratified 

 squamous. Towards the convex border of the tarsal plates the squamous type 

 gives place to the cylindrical; in the retrotarsal fossa, throughout the fornix 

 and for a short distance over the eyeball, the epithelium is exclusively columnar, 

 varying in thickness and in the number of its layers; while over the cornea 

 and adjacent parts of the sclera, the epithelium is again stratified squamous. 



The blood-vessels form an arch in each lid along the base of each 

 tarsus, between the latter and the orbicularis muscle, from which perforating 

 twigs penetrate the tarsal plates for the supply of the Meibomian glands and 

 adjacent conjunctiva. The lympliatics are arranged in two sets, a pretarsal 

 and a post-tarsal, the networks of which are connected by vessels which 

 pierce the tarsi. The former receives lymph from the skin and muscles, the 

 latter from the Meibomian glands and the conjunctiva. The nerves sup- 

 plying the eyelid include sensory, motor and sympathetic fibres. The main 

 branches lie between the tarsi and the orbicularis muscle, sending branches 

 forwards to the skin and backwards through the tarsi to the Meibomian glands 

 and the conjunctiva. Those to the conjunctiva lose their medullary coat and 

 terminate either in free arborizations, beneath or among the epithelial cells, 

 or in the end-bulbs. The latter are particularly numerous along the lid- 

 margin, but occur also in the palpebral and bulbar conjunctiva and at the 

 corneal border. The sympathetic fibres supply the tarsal and other lid- 

 glands and send filaments to the walls of the blood-vessels. 



THE LACHRYMAL APPARATUS. 



. The lachrymal apparatus consists of the gland secreting the tears, 

 situated in the anterior and outer portion of the orbital cavity, and the 

 system of canals by which the tears are conveyed from the mesial portion of 

 the conjunctival sac to the inferior nasal meatus. 



