Sir Charles Bell* says, " Anatomists have sought for a depressor of the inferior eyelid, seeing that it is depressed, but such a muscle has no existence and is quite unnecessary. The levator palpebrw superioris opens wide the eyelids, depressing the lower eyelid at the same time it elevates the upper one. If we put the finger upon the lower eyelid so as to feel the eyeball when the eye is shut and then open the eye, we shall feel that during this action the eyeball is pushed outwards. Now the lower eyelid is so adapted as to slip off the convex surface of the ball in this action and to be depressed, whilst the upper eyelid is elevated." I believe the following to be what is usually observable in regard to the motions of the lower eyelid : the lower eyelid is drawn up over the eye by a muscular exertion; when that exertion is discontinued it falls back into its former state simply by its own elasticity and that of the integuments of the cheek. It is only in the forced state of looking down wards that the prominence of the cornea forces down the lower eyelid, in the manner described by Sir Charles Bell. It is to be remembered, however, that in tie act of looking downwards, whilst the prominence of the cornea forces down the lower eyelid, the upper, contrary to what might be inferred from Sir C. Bell's state ment as quoted above, is depressed, instead of being elevated.
In winking the upper eyelid falls and the lower rises considerably.
The free margins of the eyelids are broad surfaces. That of the upper eyelid is about one-twelfth of an inch broad ; that of the lower about one-fifteenth. The edge bound ing the margin anteriorly corresponds to the insertion of the eyelashes and is round. The posterior edge is much sharper and more de fined than the preceding, and is the place where the delicate integument of the margin of the eyelid is continued into the palpebral con junctiva.
On the margin of either eyelid between the two edges or boundaries just described, but nearer the posterior than the anterior, and parallel to them, there is observable, on close inspection, a row of minute pores—the excre tory mouths of the Meibomian follicles.
The margins of the eyelids have been said to present a slope towards the eyeball, so that their outer edges only meet, when the eye is closed; and hence is produced a sort of chan nel between them and the eyeball of a triangu lar prismatic shape, which serves to lead the tears to the inner corner of the eye. Such a conformation, if it exists in the upper eyelid, is very slight and is amply compensated for by the slope in the opposite direction of the margin of the lower eyelid. The fact thus ap pears to be that when the eyelids are closed, their margins, as has been remarked by Ma gendie, meet each other surface to surface as nearly as may be.
The inner and outer corners of the eye where the eyelids join are called canthi. The outer canthus, generally speaking, forms an acute angle; but on close examination, it is observed that the apex is rounded off, some what prolonged and turned slightly down. wards. The conformation of the inner canthus is altogether peculiar and rather complicated. At the inner canthus the palpebral fissure is prolonged into a sort of secondary fissure; hence, when the eye is open, the apex of the angle formed by the inner canthus is broader and to a much greater degree prolonged than the outer; it is also rounded and turned down wards, but likewise in a much greater degree. The margins bounding the secondary fissure being destitute of cartilage are not firm and square but soft and rounded.
Where the margin of either eyelid is con tinued into the margins bounding the secon dary fissure in question, there is observed on slightly everting the eyelids a small promi nence, and in the apex of it a minute aperture, larger however than those above mentioned of the I%leibomian follicles. The eminence is called lacrymal papilla and the aperture lacry mal point.
The fissure is closed by the action of the orbicularis muscle at the same time as the eye lids; but its margins, especially at the lacrymal papillae, come completely into contact before they do. The space within the inner or nasal canthus is called lams lacrymalis. The lacry mal papillae and their points are turned in towards it, ready to take up the tears as they collect.
• At the bottom of the lacus lacrymalis, there is seen a small reddish glandular body, the lacrymal caruncle, and between the latter and the white of the eye a semilunar fold of pink coloured conjunctiva.
Eyelashes, Cilia,* Fr. Cils; Ital. Le ciglia; Germ. Die Augenwimpern. Every one knows the conformation of the eyelashes. How that they are stiff compressed hairs, increasing at first in thickness from their root, then gradu ally tapering to their free and slender extre mity; how that they spring from the anterior edge of the palpebral margins; how that those of the upper eyelid are stronger and more nu merous than those of the lower; how that those in the middle are longer than those towards the corners of the eyelids; and how that those of the upper eyelid are curved upwards and those of the lower eyelid downwards, so that their convexities regard each other. In regard to the curvature it is to be remarked that it is not gradually throughout the whole hair but is betwixt the thickest part and the root. There is another slight but variable curvature towards the extremity.