a. 4 
LACRYMAL ORGANS. 
age of the upper eyelid and the lower edge of 
that of the lower, respectively, and the cor- 
“responding edges of the orbit, there intervenes 
é : 
__acellulo-membraneous expansion. This (and 
_ im the upper eyelid, the expansion of the le- 
yator palpebre superioris,) 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 
he: art is thrown into folds. 
____ External conformation of the eyelids.—The 
_ extent and form of the eyelids are best seen 
¥ 
f 
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 
z 
‘ 
closed state of the eye, this fissure represents a 
Mere curved’ line with the convexity down- 
q h 2 eyelids are moved, it is, in the open state, 
a wide elliptical aperture. 
Me 
Be 
1 s; but on account of the way in which 
It is chiefly by the motions of the upper 
i 
4 
eyelid that the open or closed state of the eye 
is commonly produced. The upper eyelid 
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 
a the orbit, or in that morbid shortening or re- 
_ traction of the sane eyelid known by the 
" name of lagophthalmos. 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 palpebre superioris opens wide the 
eyelids, depressing the lower eyelid at the same 
Yar" Nervous System of the Human Body, 
Pp. . 
a i 
79 
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 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. Sucha 
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 ; 
