ORGANS OF SENSE. 163 
each edge called the lachrymal papilla, the point of which exhibits a minute 
but distinct foramen, the punctum lachrymale, which is the commencement 
of a small canal, the lachrymal duct, by which the tears are conveyed into 
the lachrymal sac and thence into the nose. From between the puncta the 
palpebral fissure leads inwards and enlarges into a small triangular space, 
the lacus lachrymalis, in the centre of which there is. a red papilla, the 
lachrymal caruncle, between the upper and lower lachrymal duct. The 
upper eyelid is much deeper and more movable than the lower. The free 
or ciliary margins of the palpebre are thick, firm, and abrupt, cut off hori- 
zontally so as to meet closely by flat surfaces. 
The palpebre are composed of skin, areolar tissue, an orbicular muscle, 
cartilage or fibro-cartilage, with connecting fibrous membrane, glands, and 
mucous membrane. The upper lid also has a special levator muscle, and 
the free border of each is fringed with rows of hairs or cilia. 
The skin is continuous with that of the forehead and cheek, and is of 
exceedingly delicate texture. The semilunar concentric folds, seen when 
the eye is open, are effaced when the lids are closed. The areolar tissue 
is very fine and loose, perfectly free from adipose structure. 
The cilia or eyelushes are stiff and strong. and have curved hairs placed 
in three or four rows in the cutaneous edge of the free margin; all are 
curved or bent, the superior upwards, the inferior downwards, so that when 
the lids are closed the convexities only touch, without the hairs becoming 
entangled with each other. The cilia defend the eye from the admission 
of particles of dust, minute insects, &c., and can also shade it in too strong 
a light. Along the posterior or ocular edge of each tree border is a row 
of minute foramina, the openings of the ducts of the Meibomian glands. 
The orbicular or sphincter muscle is the next tissue in the palpebre ; it 
also extends over the circumference of the orbit, superiorly into the super- 
cilia, and inferiorly into the cheeks. All the fibres are attached into the 
internal tendon, the tendo oculi or palpebrarum; this is inserted into the 
nasal process of the maxillary bone, thence it is directed outwards in front 
of the lachrymal sac, above its centre, and bifurcates. Each band incloses 
a lachrymal duct, and is inserted into the inner extremity of each tarsal 
cartilage beneath the punctum. This muscle closes the lids as a sphincter, 
by depressing the upper one considerably and raising the lower one very 
slightly, at the same time drawing it horizontally inwards. It supports the 
globe of the eye, directs the lachrymal secretion into the puncta, cleans 
and polishes the surface of the cornea; it also serves to protect the eye 
from too much light. 
The palpebral or tarsal cartilages are thin elastic plates covered by the 
orbicularis muscle on the exterior surface. The ciliary margin in each is 
abrupt and thickened, causing the firmness of the edges of the eyelids. 
The orbital edge of each is thin, and attached to the base of the orbit by a 
fibrous expansion termed the broad ligaments of the tarsus. The object of 
these cartilages is to impart strength, pliancy, and elasticity to the palpebre. 
The Meibomian glands or follicles appear on the eversion of the palpebra, 
as bony, pale, yellow, parallel ducts, leading from the free margin of each 
869 
