ANATOMY. 
59 S 
the four redli mufcles. This expanfion adlieres very clofe 
to the fclerotica, and makes it appear very white and (hi¬ 
lling ; whereas the veil of it is of a dull whitifti colour. It 
is very thin near the edge of the cornea ; in which it feerns 
to be loft, terminating very uniformly. 
The fupercilia, or eye-brows, peculiar to the human 
fpecies, are the two hairy arches lituated at the lower part 
of the forehead, between the top of the nofe and temples, 
in the fame direction with the bony arches which form the 
fuperior edges of the orbits. The (kin in which they are 
fixed does not feem to be much thicker than that of the 
reft of the forehead ; but the membrana adipofa is thicker 
than on the neighbouring parts. The fupercilia have mo¬ 
tions common to them with tliofe of the (kin of the fore¬ 
head, and of the hairy fcalp. By thefe motions the eye¬ 
brows are lifted up ; the (kin of the forehead is wrinkled 
more or le(s regularly and tranfverfely; and the hair and 
almoft the whole fcalp is moved, but not in the fame de¬ 
gree in all perfons; for fome people by this motion alone 
can move their hat, and even throw it oft' their head. The 
eye-brows have likewife particular motions which con¬ 
tract the (kin above the nofe ; and all thefe different mo¬ 
tions are performed by the occipital, frontal, and fuper- 
ciliary, mufcles. 
The palpebra; are a kind of veils or curtains placed 
tranfverfely above and below the anterior portion of the 
globe of the eye, and accordingly there are two eye-lids to 
each eye, the one fuperior and the other inferior. They 
both unite at each fide of the globe, and the places of their 
union are termed angles, one large and internal, which is 
next the nofe, the other fmall and external, which is next 
the temples. The palpebra; are made up of common and 
proper parts. The common parts are the (kin, epidermis, 
and membrana adipofa. The proper parts are the mufcles, 
the tarfi, the puntta or foramina lachrymalis, the mem¬ 
brana conjundtiva, the glandula lachrymalis, and the par¬ 
ticular ligaments which fuftain the tarfi. The tarfi and 
their ligaments are in fome meafure the bafts of all thefe 
parts. They confift of thin cartilages, forming the principal 
part of the edge of each palpebra, and they are broader at 
the middle than at the extremities. Thofe of the fuperior 
palpebrae are a little more than a quarter of an inch in 
breadth ; but in the lower palpebrae they are not above 
the (ixth part of an inch, and their extremities next the 
temples are more (lender than thofe next the nofe. 
The membrana conjunctiva is a thin membrane, one 
portion of which lines the inner furface of the palpebrae, 
that is, of the tarfi and their broad ligaments. At the 
edge of the orbit it has a fold, and is continued from thence 
on the anterior half of the globe of the eye, adhering to 
the tunica albuginea; fo that the palpebra; and the fore¬ 
part of the globe of the eye are covered by one and the 
fame membrane, which does not appear to be a continua¬ 
tion of the pericranium, but has fome connection with the 
broad ligaments of the tarfi. The name of conjun&iva is 
commonly given only to that part which covers the globe, 
the other being called fimply the internal membrane of the 
palpebra ; but we may very well name the one membra oculi 
conjun&iva , and the other membrana palpebrarum conjun&iva. 
The lachrymal gland, the ufe of which, till of late years, 
was not known, is yellowifit, and of the number of thofe 
called conglomerate glands. It lies under that deprefflon 
obfervable in the arch of the orbit near the temples, and 
laterally above the globe of the eye. It is a little flatted, 
and divided, as it were, into two Jobes ; one of which lies 
towards the infertion of the mufculus levator, the other 
towards the abdudlor. It adheres very clofely to the fat 
which furrounds the mufcles and pofterior convexity of 
the eye, and it was formerly named glandula innominata. 
The flat edge of each palpebra is adorned with a row 
of hairs called cilia, or the eye-dajkes. Thofe belonging to 
the fuperior palpebra are bent upward, and are longer 
than thofe of the lower palpebra which are bent down¬ 
ward. Thefe rows are placed next the (kin, and are not 
tingle, but irregularly double or triple. The hairs are 
longer near the middle of the palpebra; than toward the 
extremities ; and, for about a quarter of an inch from the 
inner angle, they are quite wanting. Along the fame bor¬ 
der of the palpebra;, we fee a row of fmall holes, which 
may be named foramina or puncla ciliaria. They are the 
orifices of the fame number of fmall oblong glands which 
lie in the fulci, channels, or grooves, on the inner furface 
of the tarfus. Thefe little glands are of a vvhitifh colour; 
and, when examined through a (ingle microfcope, they 
appear like bunches of grapes, thofe of each bunch com¬ 
municating together; and, when they are fqueezed be¬ 
tween two nails, a febaceous matter, like foft wax, is dif- 
charged through the pundta ciliaria. 
The puncla lachrymalia are two fmall holes in the edge 
of each palpebra, oppofite to each other, fo that they meet 
when the eye is ftuit. Round the orifice of thefe points, 
we obferve a whitilh circle, w hich feems to be a cartila¬ 
ginous appendix of the tarfus, and which keeps the orifice 
always open. Thefe two oblique circles are fo difpofed, 
that, when the eye is but (lightly (hut, they touch each 
other only toward the (kin, and not toward the globe of 
the eye. 
The caruncula lachrymalis is a fmall reddiftt granulated 
oblong body, fituated precifely between the internal angle 
of the palpebra; and globe of the eye, but it is not flelhy, 
as its name would infinuate. The fubftance of it feems 
to be wholly glandular; and it appears through a fingle 
microfcope in the fame manner as the other conglomerate 
glands. We difeover on the globe of the eye, near this 
glandular body, a femilunar fold formed by the conjunc¬ 
tiva, the concave fide of which is turned to the uvea, and 
the convex fide to the nofe. This fold, which has the 
name of membrana femilunaris, appears mod when the eye 
is turned toward the nofe; it is (haped like a crefcent, the 
two points of which anfwer to the punfta lachrymalia, and 
conduct the tears into the pundla. 
The mufcles which move the palpebra; are commonly 
reckoned to be two. In man, the fuperior palpebra has 
much more motion than the inferior. The fmall fimple 
motions, called twinkling, which frequently happen, tho* 
not equally often in all (ubjeCts, are performed by the al¬ 
ternate contraction of the levator palpebrae and orbicularis. 
The external carotid artery, and the temporal and fron¬ 
tal arteries, give feveral ramifications to the integuments 
which furround the eye; the internal carotid, having en¬ 
tered the cranium, fends off a confiderable branch called 
the ocular, which accompanies the optic nerve, to be dis¬ 
tributed to the mufcles and globe of the eye, to the leva¬ 
tor palpebrae, to the fat, glandula lachrymalis, membrana 
conjundtiva, caruncula lachrymalis, &c. The veins of 
all thefe parts anfwer nearly to the arteries; thofe of the 
globe of the eye are called vafa vorlicofa. The internal 
veins unload themfelves, partly into the internal jugular 
vein, by the finus cavernofi; and partly into the external 
jugular vein, by the vena angularis, or maxillaris externa, 
the maxillaris interna, temporalis, See. 
Befides the optic nerve, the globe of the eye receives 
feveral fmall ones, which run on each fide along and about 
the optic nerve, from its entry into the orbit to its infer¬ 
tion in the globe. Thefe fmall nerves, which run from 
behind forward, between the fclerotica and the choroides, 
have formerly been taken for particular ligaments by ana- 
tomiftsof confiderable eminence, but are now known un¬ 
der the name of ciliary nerves. 
The eye being the "organ of vifion, the greater part of 
it is compofed of pellucid humours capable of refradting 
the rays of light. The complexity of this organ is ne- 
ceflary for the defence of its tender parts ; and the diver- 
fity of the feveral humours, together with the various of¬ 
fices which this curious machine- performs, neceff'arily re¬ 
quired a very compound inftrument. The perpetual 
attrition of the eye lids afeending and defeending againft 
the globe of the eye, is prevented by the tears ; which 
preferve alfo the tendernefs ot the membranes and of the 
cornea, and ferve to vvalh out any infedts or other (harp 
corpufcles. 
