STEUCTUEE OF THE CONJUNCTIVA. 



585 



Fi". 39; 



'. — ^Ieibomian Glands of the Left 

 Eyelids as seen from behind. 



orbicularis muscle, attached ])eriplierally to the margin of the orbit, 

 and internally to the tarsi, with which its tissue is continuous. The 

 membrane is thickest at the outer part of the orbit. 



On the ocular surface of each lid are seen from twenty to thirty 

 parallel vertical rows of yel- 

 low granules, lying im- _^ Fig. 397. 

 mediately under the conjunc- 

 tival mucous membrane, and 

 known as the Meibomian 

 fjIandsi^g.Sdl, G,G). They are 

 compound sebaceous glands, 

 imbedded in grooves at the 

 back of the tarsi ; and they 

 open on the free margin of 

 the lids by minute orifices, 

 generally one for each. The 

 glands consist of nearly 

 straight tubes, closed at the 

 end, with numerous small 

 cJBcal appendages projecting 

 from the sides. The tubes 

 are lined for some distance 

 by stratified epithelium con- 

 tinuous with that of the skin : 

 the glandular recesses have a 

 lining of cubical epithelium 

 and are filled with the fatty 

 secretion. According to 

 Colosanti the glands have a basement membrane, and a muscular 

 layer outside this: he further describes a network of fine nervous 

 fibrils amongst the epithelium cells. 



A layer of unstriped muscular tissue is contained in each eyelid ; that of the 

 upper arising from the under sui-face of the levator palpebra3, that of the lower 

 from the neighboLU'hood of the inferior oblique muscle, and each being inserted 

 near the margin of the tarsus. A few fibres are also to be found in the plica 

 semilunaris (H. Miiller). It may also be mentioned in this place that the same 

 writer describes a layer of unstriped muscle crossing the spheno-maxillary 

 fissure, corresponding to a more largely developed layer found in the extensive 

 aponeurotic part of the orbital wall of various mammalia. This set of fibres has 

 been more particularly described by Ttu'uer.* 



The eyeJasTies (cilia) are strong short curved hairs, arranged in two or 

 more I'ows along the margin of the lids, at the line of union between 

 the skin and the conjunctiva. The upper lashes are more numerous 

 and longer than the lower, and are curved in an opposite direction. 

 N"ear the inner canthus the hairs are weaker and more scattered. Imme- 

 diately within the eyela.shcs, between them and the muscle of Eiolan, 

 is a row of large modified sweat-glands, which open into the mouths of 

 sebaceous glands (not the Meibomian). 



Structure of the conjunctiva. — The conjunctiva consists of the 

 palpebral part, Avitii which may be included the plica semilunaris and 



* H. Midler ia Zeitschr. f. wiss, Zool. 1858, p. 5il ; W. Turner, in Nat. Hist. Eev 

 1S'J2, p. lOtJ. 



a, a, palpebral conjunctiva ; 1, lachrymal gland ; 

 2, openings of seven or eight of its ducts ;-3, 

 xipper and lower puncta lachr^nnalia ; 6, 6, ends 

 of the upper and lower Meibomian glands, of 

 which the openings are indicated along the 

 margins of the eyelids. 



