ORGANS OF THE BODY. 



649 



The posterior surface of the eyelids, and anterior portion of the sclerotic, 

 with the cornea, are covered by a thin, soft, mucous membrane, known as 

 the conjunctiva. This is generally divided into the c. paJpebrantm, the c. 

 bulbi, or that passing from the' latter to the ball of the eye; and the 

 inferior part, the c. scleroticce and cornece. The latter portion, however, 

 deserves no longer the name of mucous membrane, from the fact of its 

 being represented merely by a laminated flattened epithelial covering. 



The substratum of the palpebral conjunctiva is formed of reticulated con- 

 nective-tissue containing lyuiphoid cells (Henle). This Stieda asserts to 

 be separated from the epithelial layer by a homogeneous elastic membrane. 

 The epithelium in the cleft between the lids, derived from, the cuticular 

 layer of the skin, was formerly erroneously supposed to be ciliated (Henle). 

 It consists, on the contrary, of several layers of pavement cells. 



Numerous depressions, pits, and clefts, of the most diverse forms, which 

 occur in this mucosa, are, strange to say, lined by a kind of columnar 

 epithelium, producing the deceptive appearance of true glands ; indeed, such 

 were described here by Henle. Among the ordinary epithelial elements 

 of the part there occur also, in the conjunctiva palpebrarum, those struc- 

 tures known as beaker cells (Stieda). We also meet here with tactile 

 corpuscles, according to Krause, the terminal structures of the nerves of 

 sensation ( 185). The conjunctiva bulbi is a continuation, not only of the 

 epithelial cellular layer, but also of the subjacent connective-tissue. The 

 first extends over the whole cornea ( 292), but not so the latter, which 

 is lost at the periphery of the cornea in the tissue of the same, after having 

 become very thin. The plica semilunaris, finally, is a duplicature of the 

 conjunctiva bulbi, and contains in its caruncula lacliryinalis ordinary 

 sebaceous glands. Scattered fasciculi of unstriped muscle 

 also occur here (H. Mutter). 



The glands of the conjunctiva are of various kinds. 



In man, and in certain of the mammalia, in the first 

 place, small racemose glandules are to be found, known 

 generally as mucous glandules (" accessory lachrymal 

 glands" of Henle). They are situated in that portion of 

 the conjunctiva passing from the tarsus to the bulb, and 

 are seen to the number of 42 in the upper, while from 

 2 to 6 only occur in the lower lid. They are irregularly 

 scattered, imbedded in the mucous membrane or sub- 

 mucous tissue. They are most crowded in the transition 

 fold. The contents of their acini, which are about 0'0564 

 mm. in diameter, present fatty particles. 



Among the ruminants, but not in man, there occurs, 

 as was discovered some years ago by Meissner, a second 

 very interesting form of gland in the conjunctiva of the 

 eyeball, and particularly in that part encircling the cornea 

 below and internally. This belongs to the convo- 

 luted tubular class (tig. 601) like the sweat glands of 

 the skin, but each gland opens with a bulbous dilata- 

 tion. The number of such convoluted glandules, how- 

 ever, is very small, only amounting in each eye to from 

 6 to 8. 



At the outer border of the cornea of the pig another 

 third species of gland was found by Manz. IP this form we have simple, 

 round, or oval sacs, measuring 0-067-0-2 mm. in diameter, made up of 



601. A convo- 

 luted gland from 

 the conjuuctivu 

 bulbi of the calf 

 (after Manz). 



