AESTHESIOLOGY 
THE SENSE ORGANS AND COMMON INTEGUMENT 
The organs of the senses (Organa sensuum) receive external stimuli and con- 
duct impulses to the brain which result in sensations of sight, hearing, taste, smell, 
and touch. They consist essentially of specially differentiated cells (neuro-epithe- 
lium) and a conduction path which is simple in the more generalized sense organs, 
elaborate in those which are highly specialized—the eye and the ear. 
THE SENSE ORGANS AND SKIN OF THE HORSE 
THE EYE 
The eye or organ of vision (Organon visus) in the broader sense of the term 
comprises the eyeball or globe of the eye, the optic nerve, and certain accessory 
organs associated therewith. The accessory organs (Organa oculi accessoria) are the 
orbital fascize and muscles, the 
eyelids and conjunctiva, and Upper eyelid 
the lacrimal apparatus. These Third eyelid ; 
structures will be considered in Caruncula, \ 
the order in which they may be lacrimalis \ 
most conveniently examined Ho 
- ? canthus >, 
taking the horse asa type. The ay 
bony walls of the orbit have 
been described in connection 
with the skull; the periorbita, 
a fibrous membrane which en- 
closes the eyeball together with 
its muscles, vessels, and nerves, 
may be appropriately included 
in the account of the fascie. 
“7 . 
THE EYELIDS AND CONJUNC- \ 
ae Lower eyelid 
The eyelids, upper and Fic. 688.—Lerr Ere or Horse. 
lower (Palpebra superior et in- 9, Zygomatice arch; 10, supraorbital depression; 12, supraorbital proc- 
ferior), are movable folds of ess; 27, facial crest. (After Ellenberger-Baum, Anat. fiir Kunstler.) 
integument situated in front 
of the eyeball. When closed, they cover the entrance to the orbit and the 
anterior surface of the eyeball. The upper lid is much more extensive and 
more movable than the lower one, and its free edge is more concave. The 
interval between the lids is termed the palpebral fissure (Rima palpebrarum). 
When the eye is closed, it is an oblique slit about two inches (ca. 5 cm.) 
in length; when open, it is biconvex in outline. The ends of the fissure are 
the angles or canthi, and are distinguished as medial or nasal, and lateral or 
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