OBSERVATIONS ON SOUNDNESS. 
263 
it is pale in colour,/and is of an irregular shape; it is a con¬ 
glomerate gland, very much resembling externally the salivary 
glands; its office is to secrete the tears, which are conveyed 
by its ducts upon the conjunctiva, where they become dif¬ 
fused in two wa 3 "S, namely, by their owm gravity and also 
by the motion of the lids. The tears are of a saline cha¬ 
racter, and possess irritating properties, often observed in 
ophthalmia. 
The cartilago-nictitans is a concavo-convex body, lodged 
behind the inner canthus, betw’een the globe and side of the 
orbit; it is covered by conjunctiva, and is attenuated on its 
anterior extremity; it is imbedded in adipose substance; its 
action is principally mechanical. The late Mr. Liston in¬ 
formed me, when examining me for my diploma, that he had 
discovered two small muscles which aided in performing its 
movements; the names of them I doffit remember. Its use 
is to dislodge anything foreign on the eye. 
Puncta lachrymalia are two small openings piercing the 
inward margins of the two lids near the root of the caruncula 
lachrymalis; the superior is smaller than the inferior. 
The ductus ad nasum is the canal intended for the passage 
of the tears from the eye to the nose; it passes through the 
lachrymal bone, between it and the anterior turbinated bone, 
to the cuticular surface of the inner and low’er part of the 
nostril; its terminating upon cuticular membrane is to 
prevent the tears from irritating the mucous surface. 
The arteries which supply the globe of the eye are the 
ophthalmic and the arteriaTcentralis retinae. The appendages 
are supplied by the internal maxillary. These several parts 
are well taken care of by the large amount of adipose sub¬ 
stance found in the orbital cavity; the case itself is lined by 
a dense membrane, said to be a continuation of the dura 
mater. The fatty matter being in a semifluid state during 
the life of the animal, admits of the various movements which 
the eyes of the horse are called upon to perform, and it is the 
absence of this fatty substance, through absorption, which 
gives to young animals the appearance of old age. 
The globe of the eye is regarded as an optical instrument of 
very complex construction, beautifully arranged and adapted, 
into which the rays of light are received, and by the medium 
of which agent the horse is able to take cognisance of the 
form, size, colour, and position of bodies that transmit or 
reflect it. The globe is placed in the cavity of the orbit most 
laterally and obliquely, which cavity is formed of eight bones ; 
the two cavities are formed of fourteen bones; four form the 
outer—the frontal, malar, unguis, and squamous-temporal 
