1444 HUMAN ANATOMY. 



ineffaceable transverse creases which, with advancing years, are supplemented by 

 vertical furrows. Towards the inner canthus, particularly in the lower lid, pigment 

 exists in variable quantity, often in amount sufficient to confer a distinct brownish 

 hue to the integment. 



The subcutaneous tissue is distinguished by the entire absence of fat, its loose 

 texture and great extensibility and elasticity. In consequence of these properties, it 

 sometimes becomes the seat of extensive swelling after edema or hemorrhage. 



The muscular layer, for the most part consisting of the annular bundles of the 

 orbicularis palpebrarum, is in fact so blended with the subcutaneous tissue as to be 

 practically embedded within the latter. Reference to the description of the orbicu- 

 laris palpebrarum (page 484) will recall the general division of the muscle into 

 an orbital and a palpebral portion, and the relations of the deeper or lachrymal slip 

 (tensor tarsi) to the tear-sac and the tarsal plate. In vertical sections of the eyelid 

 (Fig. 1201) the circularly arranged bundles of the palpebral portion show as 

 transversely cut groups of muscle-fibres enclosed by condensations of the surround- 

 ing areolar tissue. A distinct annular tract, known as the ciliary bundle (m. ciliaris 

 Riolani} lies close to the free border of the lid, chiefly between the tarsal plate and 

 the hair follicles, but in part often also between the conjunctiva and the tarsus. In 

 the upper lid, in addition to the circular bundles of the orbicularis palpebrarum, the 

 terminal strands of the longitudinal fibres from the levator palpebrae superioris 

 descend along the deeper surface of the first-named muscle. Some of these 

 penetrate between the circular bundles and end in the deeper layer of the skin ; 

 others descend more vertically to find their insertion in the upper border of the 

 tarsal plate. 



Under the name, tarsal muscles or muscles of Mi/ller, are described the un- 

 certain bundles of involuntary muscle that are found in the vicinity of the convex 

 border of the tarsi. Those within the upper lid arise from the tendon and inter- 

 mingle with the fibres of the levator palpebrae, with the course of which they 

 agree, and end either by insertion into the upper border of the tarsal plate, or into 

 the adjacent fibrous tissue. In the lower lid, they are less numerous and regular, 

 and extend from the fornix conjunctive to the adjacent border of the tarsus. The 

 tarso-fascial layer is represented next the margins of the lids by the tarsal plates and 

 beyond the latter by the septum orbitale. 



The tarsal plates (tarsi) are two lamellae of dense fibrous tissue, one in each 

 lid, that occupy the margins of the eyelids, to the maintenance of whose form they 

 largely contribute. They are crescentic in outline, the borders next the lid-cleft 

 being only slightly curved and almost straight and the thinner distal borders mark- 

 edly convex. Their ends are joined to the palpebral ligaments which branch into 

 upper and lower limbs for the attachment of the tarsal plates. The upper tarsus is 

 the more arched and broader, measuring about 10 mm. or about double the lower 

 plate, in both cases the median ends of the crescents being blunted and less pointed 

 than the lateral. The plates are approximately i mm. in thickness and consist of 

 densely felted fibrous tissue, and are blended in front and below with the subcu- 

 taneous tissue, above with the septum orbitale and the insertion of the lid-muscles, 

 and behind with the conjunctiva. 



In addition to preserving the curvature of the lids, the tarsal plates lodge the 

 linear series of the Meibomian or tarsal glands (glandulae tarsalcs). These struc- 

 tures, between thirty and forty in number in the upper lid and about one-third less 

 in the lower one, consist of a chief tubular duct, placed vertically and lined by stratified 

 squamous epithelium, which is beset with numerous simple or branched, irregular, 

 flask-shaped alveoli. The latter contain cuboidal epithelial elements that resemble 

 in appearance and condition those found in sebaceous follicles, to which class, in fact, 

 the tarsal glands belong. They secrete an oily substance, sebum palpebrarum, which 

 is discharged through the minute punctiform orifices of the ducts that, on everting 

 the edges of the lids, are seen as a row of dark points just external to the sharp con- 

 junctival border of tin- eye-lid. In this manner the latter is kept lubricated, and thus, 

 under usual conditions, maintains an effective barrier against the- overllow of the 

 tears from the conjunctiva! sac. Within the free edge of the eyelids, just in advance 

 of the tarsal plates, lie the glands of Moll, and the glands of Zeiss The former 



