LACRYMAL ORGANS. 



79 



lage of the upper eyelid and the lower edge of 

 that of the lower, respectively, and the cor- 

 responding edges of the orbit, there intervenes 

 a cellulo-membraneous expansion. This (and 

 in the upper eyelid, the expansion of the le- 

 vator palpebrae superiors,) together with the 

 conjunctiva on its inside and the skin on its 

 outside, serves as it were the office of a loose 

 hinge for the firm part of the eyelid. But the 

 pivots on which the motions of the eyelids, 

 especially of the upper, more immediately take 

 place, are the angles of the eye. The upper 

 eyelid, indeed, moves somewhat in the manner 

 of the visor of a helmet, its firm part, when 

 the eye is open, being drawn up and retracted 

 within the margin of the orbit whilst its loose 

 part is thrown into folds. 



External conformation of the eyelids. The 

 extent and form of the eyelids are best seen 

 when they are closed in sleep. The convexity 

 of their external surface then bespeaks a cor- 

 responding concavity of the internal adapted 

 to the prominent front of the eyeball. The 

 opening between the two eyelids is called the 

 palpebral fissure, rima palpebrarum. In the 

 closed state of the eye, this fissure represents a 

 mere curved line with the convexity down- 

 wards ; but on account of the way in which 

 the eyelids are moved, it is, in the open state, 

 a wide elliptical aperture. 



It is chiefly by the motions of the upper 

 eyelid that the open or closed state of the eye 

 is commonly produced. The upper eyelid 

 is larger than the lower, and in the closed 

 state of the eye from relaxation simply, as 

 during sleep or in death, it covers much more 

 of the front of the eyeball than the lower. 

 But in forced closure of the eye by the action 

 of the orbicularis palpebrarum muscle, the 

 lower eyelid is drawn up, being impressed at 

 the same time with a horizontal movement to- 

 wards the inner angle, and meets the upper 

 half-way, so that the latter cannot descend so 

 far as it does during sleep. Hence, in active 

 closure of the eye the skin of the upper eyelid 

 is thrown into folds, whereas, in passive clo- 

 sure, it is smoothly extended in a convex form 

 over the eyeball. The lower eyelid is capable 

 of pretty extensive motion. It can of itself 

 alone cover almost entirely the whole front of 

 the eyeball, either when the upper eyelid is 

 held immoveably retracted under the edge of 

 the orbit, or in that morbid shortening or re- 

 traction of the upper eyelid known by the 

 name of lagop/itfutlmos. But as the covering 

 of the eye by the lower eyelid is always the 

 effect of a muscular exertion, the eye in lagoph- 

 thalmos will not be covered during sleep, 

 hence the lower can never serve as a substitute 

 for the upper eyelid . 



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 palpebne superioris opens wide the 

 eyelids, depressing the lower eyelid at the same 



* The Nervous System of the Human Body, 

 p. 186. 



time it elevates the upper one. If we put the 

 finder 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 the 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; 



