ANATOMICAL CONSIDERATION'S. 



35 



tion against so terrible an affliction, which would expose any wild 

 animal to a fearful death. The outer mem- 

 brane of the eye is almost limited to cover- 

 ing the more forward or transparent surface, 

 being thence reflected upon the interior of 

 the eyelids. This membrane, when in a 

 single layer, is incapable of communicating 

 to the sensorium more than a feeling of un- 

 easiness. When single, it may be touched, 

 burnt, and cut, without producing actual 

 pain ; but the unpleasant sensation provokes 

 a desire to wink, and the instant the lid 

 descends upon the globe, or from the mo- 

 ment when two surfaces of the membrane 

 are in apposition, agony ensues. 



The membrane now under consideration 

 renders it an impossibility for any substance 

 to get "into the eye;" the pain present, 

 when such an assertion is commonly made, 

 gives the strongest proof that the foreign 

 body is retained between two surfaces of 

 that delicate structure which is called con- 

 junctiva. Dryness is, however, destructive of the feeling and of the 

 transparency of this membrane. Nature, therefore, has created a special 

 gland for assuring its perpetual moisture. This last body is situated 

 immediately beneath the surface, under the upper lid and toward the 

 outer corner of the eye. It is, on ordinary occasions, stimulated to 

 send forth its secretion by the act of winking; and the outer corner 

 being situated above the inner corner of the horse's eye, the moisture 

 is, by the motion of the lid, instantaneously brushed over the circular 

 globe. 



The gland of the horse, however, has a distinct use not shared by any 

 similar provision to be found in the eye of man. In the human being, 

 grief or pain provokes the secretion ; these are always accompanied by 

 floods of tears. Some writers assert they have witnessed agony induce 

 tears in the quadruped ; but the author has seen fearful operations in- 

 flicted on the noble animal — he has heard huge groans testify to the 

 sufferings endured ; yet he has never beheld the eye overflow, or seen 

 anything present which approximated to weeping. 



Pain, wben occasioned by some foreign body between the two layers 

 of membrane, produces not weeping, but a positive overflow of Uquid, 

 the purpose of which will be best explained after the reader has been 



DIAGRAM, EXPLANATORY OP THE SITUA- 

 TION OF THE LACHRYMAL GLAND. OR 

 THE SOURCE OT TEARS, AND OF OTHER 

 PARTS PROPER TO THE HORSE'S EYE. 



a. Tlie outer angle. 6. The puncta 

 lachrymalis, or rouud body, situated at 

 the inner angle of the eye. c. The lach- 

 rymal gland, covered by the upper lid 

 and placed near the outer angle of the 

 eye. e e. The position, extent, and 

 doubling of the conjunctiva, or of the 

 investing mucous membrane, which 

 envelops the outer portion of the 

 globe and lines the lids. 



