The skin of the eyelids is continuous with and similar to that of the face, only some what more delicate. The skin of the upper eyelid is more delicate than that of the lower.
The eyebrows, supercilia, Fr. Les sourcals ; Ital. Le sopraeiglin; Germ. Die Augenbraunen (fig. 11). The external appearance of the eye brows is too well known to require any particu lar description. Their prominence is produced partly by the superciliary arches of the frontal bone over which they lie, but principally by a cushion of cellular and adipose tissue under neath the skin, together with the roots of the hairs and muscular substance. The hairs of the eyebrow are, generally speaking, directed from within outwards, but internally, especi ally where they exist over the root of the nose, they are inclined in the opposite direction. Those immediately over the root of the nose indeed cross each other. Besides the general direction from within outwards of the majority of the hairs of the eyebrows, it is to be re marked that the uppermost ones are inclined downwards and the lowermost ones upwards, so that they are raised into a kind of ridg: along the middle line of the eyebrow, an ar rangement which presents a pleasing appear ance of regularity. The eyebrows are eapabt of very free motions, and these are in clos connexion with the affections of the mind hence the eyebrows have always been con sidered a very important physiognomonic. feature. The movements of the eyebrow are effected by muscles inserted into their skin These muscles are: the frontalis, which elevate the eyebrows ; the upper and outer fibres • the orbicularis palpebrarum, which depres them, and the corrugatorsupercilii, which draw them inwards. For their description, se article FACE.
The eyelids act in conjunction with the iri on many occasions ; thus, in a weak light an. in the act of looking at distant objects, th eyelids are widely opened at the same time tha the pupil is dilated ; when the eye is to a strong light, on the contrary, or in lookin at near objects, the palpebral fissure is con tracted along with the pupil. In sleep corn plete closure of the eyelids is associated wi very great contraction of the pupil.* Internal structure rf the eyelids.—The tar
sal cartilages may be looked upon as the skele ton of the eyelids, and the membraneous ex pansion intervening between them and the mar gins of the orbits as connecting ligaments. The latter, indeed, are called the tarsal ligaments, although they do not in reality possess a liga mentous structure, but consist merely of dense laminar cellular membrane. On the inner sur face of the tarsal cartilages and tarsal ligaments the palpebral conjunctiva adheres. On the outer surface are the palpebral and ciliary por tions of the orbicularis palpebrarum muscle, over which is the skin. Moreover, incorporated with the superior tarsal ligament is the expan sion of the tendon of the levator palpebra• supe rioris muscle. Imbedded in the substance of the tarsal cartilages lie the Meibomian follicles. Underneath the skin and the ciliary portion of the orbicularis palpebrarum muscle, the roots of the eyelashes lie close on the tarsal cartilages.
cartilages.—,Tarsi ; Fr., Les 'Parses; Ital., I tarsi ; Germ., Der ilagenliedknorpel. These are thin plates of fibro-cartilage, convex on the outer surface, concave on the inner, to be adapted to the front of the eyeball. The upper is the larger. One of their margins is thick and straight, the other thin and curved, especially so in the upper, which therefore re presents in some degree a segment of a circle, whilst the lower is little more than a narrow stripe. The thick and straight margin, called the ciliary, forms the margin of the eyelid; the thin and curved margin, called orbital, degene rates into the membraneous expansion already mentioned under the name of tarsal ligaments. Towards the outer canthus the orbital margins of the tarsal cartilages run into the ciliary ones at an acute angle, whilst towards the inner can thus they form an obtuse angle by their junc tion. The transverse length of the tarsal carti lages is somewhere about an inch, the breadth of the upper cartilage at its broadest part about one-third of an inch, the breadth of the lower cartilage only half as much. At the inner can thus the tarsal cartilages extend no farther than the lacrymal points, and at the outer canthus they stop close to the commissure of the two lids.