THE EYELIDS AND CONJUNCTIVA. 1445 



are coiled tubules, resembling modified sweat glands, the latter sebaceous glands, 

 the ducts of which usually open close to or into the mouths of the follicles of the 

 eye-lashes. 



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 continu- 

 ously with the secretion of the tear-gland, assumes the translucently rosy tint and 

 general appearance of a mucous membrane, as which the conjunctiva is often 

 regarded. 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 yellowish stripes. On gaining the retrotarsal fossa, along the 

 convex border of the tarsal plates, the conjunctiva becomes loose and movable and 

 marked by circular folds since the tunica propria, which here connects the epithelium 

 with the underlying fascial tissue, is plentiful. Small tubules, the glands of Henle, 

 often occupy the sub-epithelial tissue of this part of the conjunctiva. In the fornix 

 and its vicinity minute lymph-nodules occur normally, 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, being 

 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, unwrinkled but gradually thinning, as far as the 

 corneal margin, at which point {limbus cornea} the tunica propria ends and the 

 epithelium alone continues uninterruptedly over the cornea. During its passage from 

 the free edge of the eyelid to the cornea, the character of the conjunctiva! 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 way to the 

 cylindrical ; in the retrotarsal fossa, throughout the fornix and for a short distance 

 (.5-1 mm.) over the eyeball, the epithelium is exclusively columnar, varying in 

 thickness and in the number of its layers ; whilst over the cornea and adjacent parts 

 of the sclera, the epithelium is again stratified squamous. 



Vessels of the Eyelids. The arteries chiefly supplying the eyelids are the 

 superior and inferior palpebral branches from the ophthalmic and from the lachrymal 

 arteries. These form the first source, the internal palpebral, which arise either sepa- 

 rately, or by a short common stem, pierce the septum orbitale a short distance above 

 or immediately below the internal palpebral ligament, and, in addition to sending 

 twigs to the lachrymal caruncle, canals and sac, pursue a tortuous course near the 

 free margin of the lids towards the external canthus. On nearing the latter the 

 superior and inferior internal branches join the corresponding branches from the 

 external palpebral and from the lachrymal, as well as anatomosing with twigs from the 

 superficial temporal and transverse facial arteries. In this manner a tarsal arch is 

 formed in each lid along the base of each tarsus, between the latter and the orbicu- 

 laris muscle, from which perforating twigs penetrate the tarsal plates for the supply of 

 the Meibomian glands and the adjacent conjunctiva. In the upper lid a less regular 

 secondary tarsal arch is formed along the convex border of the tarsus by the anasto- 

 mosis of the palpebrals and the frontal and supraorbital branches. A similar, but less 

 constant and complete, arch occurs in the lower lid. 



In consequence of the double path of escape of the blood from the orbit through 

 the ophthalmic and the facial veins the veins of the eyelids are tributaries of two 

 systems. Those from the deeper structures (conjunctiva, Meibomian glands), the 

 retrotarsal veins, empty into the branches of the ophthalmic, while those draining the 

 more superficial parts of the eyelid, pretar sal veins, are tributary to the frontal and facial 

 veins medially and to the supraorbital and superficial temporal laterally. Since not 

 only the supraorbital, but also the frontal veins communicate with the ophthalmic 

 system, the blood is carried off by way both of the orbital and facial channels. 



The lymphatics of the eyelids are arranged in two sets, a pretarsal and a post- 

 tarsal, the net-works of which are connected by vessels which pierce the tarsi. The 



