758 SPECIAL HISTOLOGY. 



junctiva. The skin is here very thin (1-5-1-8 of a line), with scanty, 

 subcutaneous connective tissue containing no fat, a delicate cuticle, 

 0-055-0-058 of a line thick, and short papilla (of 0-060-0-066 of a line) ; 

 but it is furnished throughout with minute sudoriparous glands (of 1-10 

 1-12 of a line) and almost invariably, with numerous minute hairs (fre- 

 quently, with contiguous sebaceous glands, but whether always so pro- 

 vided I do not know). At the edges of the palpebrce these hairs are more 

 considerably developed and constitute the eyelashes, which are also fur- 

 nished with sebaceous follicles. Agreeing in all respects, in structure 

 and secretion, with the sebaceous glands, the Meibomian glands, never- 

 theless, differ somewhat in form. They are imbedded in the tarsal car- 

 tilages, to the number of from twenty to forty, in the form of elongated, 

 white, delicate, parallel, racemose follicles, disposed in such a direction 

 that the long axes of the glands, cut those of the tarsal cartilages at a 

 right angle. Each of these glands which are visible at once upon 

 inverting the eyelid, and do not occupy the entire width of the tarsi, 

 consists of a straight excretory duct, 0-04-0*05 of aline wide, which at its 

 orifice on the inner edge of the free palpebral border, is lined with com- 

 mon epidermis, including the horny and the mucous layers, and more 

 internally presents the usual structure observed in the sebaceous glands. 

 This canal, throughout its length, is beset with round or pyriform, shortly 

 pedunculated, gland-vesicles, 0-04-0-07-0-1 of a line in diameter, either 

 isolated or aggregated several together, in which, in a mode similar to that 

 already described in speaking of the sebaceous glands ( 74), a constant 

 production of spherical, adipose cells, 0-005-0-01 of a line in size, takes 

 place ; the cells differing from the sebaceous cells, only in the circum- 

 stance that the oil-drops contained in them do not usually run together 

 into a single large drop, but remain separate. As these cells advance 

 towards the excretory duct they gradually break up into a whitish pul- 

 taceous substance composed of oil-drops, and form the so-termed lema 

 s. sebum palpebrale. The orbicularis palpebrarum, constituted of trans- 

 versely striped, though rather slender and pale muscular fibres, lies im- 

 mediately beneath the skin, its stratum internum being separated from 

 the tarsi by a layer of lax, and to some extent adipose connective tissue, 

 so that it may be readily raised into a fold together with the integuments. 

 It is only towards the free margin that this muscle is more closely 

 attached to the tarsi, and there presents a bundle of fibres situated at 

 the very verge of the eyelid, which is parted from the rest of the muscle 

 by the follicles of the cilia the so-termed ciliar muscle (musculus cili- 

 aris, Riolan). 



The conjunctiva (a mucous membrane), commences at the free palpe- 

 bral margin, as an immediate continuation of the external integument, 

 lines the posterior surface of the eyelids, and is then reflected upon the 

 eyeball, investing the anterior part of the sclerotic and the entire cornea. 



