THE SENSE ORGANS AND SKIN OF THE HORSE 
temporal (Angulus oculi medialis, lateralis). The lateral angle is rounded when the 
eye is open, but the medial angle is narrowed and produced to form a D-shaped 
bay or recess, termed the lacrimal lake (Lacus lacrimalis). In this there is a rounded 
pigmented prominence known as the lacrimal caruncle (Caruncula lacrimalis); it 
is about the size of a small pea, and is covered with modified skin, connected with 
that of the medial commissure, from which project a number of hairs provided with 
sebaceous glands. The lids unite on either side and form the commissures, medial 
and lateral (Commissura palpebrarum 
medialis, lateralis). The anterior sur- 
face of the lids (Facies anterior palpe- 
brarum) is convex and is covered with 
very short hair. A considerable num- 
ber of tactile hairs are scattered over 
the lower part of the lower lid, but on 
the upper lid they are very scanty. 
The infrapalpebral depression (Sulcus 
infrapalpebralis) indicates somewhat 
indistinctly the limit of the lower lid. 
The upper lid is marked by two fur- 
rows when raised. The posterior sur- 
face (Facies posterior palpebrarum) is 
adapted to the free surface of the eye- 
ball and is covered by the palpebral 
conjunctiva. The free border of the 
lid is smooth and usually black. It 
has a well-defined posterior margin 
(Limbus palpebralis posterior), along 
which the ducts of the tarsal glands 
open. The anterior margin (Limbus 
palpebralis anterior) bears stiff hairs 
termed the cilia (eyelashes). On the 
upper lid the cilia are long and num- 
erous except at its medial third, where 
they are very small or absent. On 
the lower lid the cilia are often scarcely 
distinguishable from the ordinary hairs; 
in other cases they may be clearly seen 
1, Tarsal gland of upper lid; 2, palpebral conjunctiva; eXcept near the lateral canthus, and 
}, fornix conjunctive; 4, levator palpebre superioris; 5, are much finer and shorter than those 
orbieuleris-ooult) /@,.cormeai, 7, Snteror ehamber; 4)4ne; of this upper lid. The edge of each lid 
&, 9", granula iridis; 10, posterior chamber; 11, ciliary proc- A ‘ 
ess; 12, ciliary muscle; 13, ciliary zone or suspensory 18 pierced near the medial angle by a 
lig. of lens; 14, chorioid; 15, sclera; 16, lens; 17, root of | minute, slit-like opening, the punctum 
i a a as lacrimale, which is the entrance to 
the lacrimal duct. 
The skin of the eyelids is thin and freely movable, except near the free edge, 
where it is more firmly attached. The underlying subcutaneous tissue is destitute 
of fat. The muscular layer consists chiefly of the elliptical bundles of the orbicu- 
laris oculi, with which are associated fibers of the corrugator supercilil in the upper 
lid and the malaris in the lower lid. At the medial side there is a fibrous band, the 
palpebral ligament, which is attached to the lacrimal tubercle and furnishes origin 
to some fibers of the orbicularis. At the medial commissure a bundle detached 
from the orbicularis passes inward behind the lacrimal sac, and is known as the pars 
lacrimalis (or Horner’s muscle). At the lateral side an indistinct palpebral raphé 
occurs where fibers of the orbicularis decussate. The fibrous layer is thicker and 
I'ic. 689.—Verticat Section oF ANTERIOR Part oF EYE 
oF Horse, with Lips HaLr CLosEp. 
