3fi 



ANATOMICAL CONSIDERATIONS. 



made acquainted witli a particular organ situated at tlie inner angle of 

 tlie eye. 



Tlie lower corner of the organ is characterized by a round body, 

 which, being enveloped in a single layer of membrane, is strictly with- 

 out sensation. Upon this body the grime of the human eye accumu- 

 lates, and we shall shortly perceive that 

 its presence in the horse is not without 

 a purpose. Next to the foregoing de- 

 velopment, and so placed as to accu- 

 rately fit the globe, is a structure which 

 anatomists name the cartilage nictitans, 

 or the winking cartilage. The more 

 forward portion of this cartilage pos- 

 sesses a fine edge, while its base pre- 

 sents a broad surface, which reposes 

 upon the fat at the back of the orbit. 

 Now, as fat is not compressible by 

 ordinary force, whenever the muscles draw the globe backward, the 

 adipose matter is driven forward ; this last carries with it the cartilage 

 nictitans, which is consequently projected suddenly over the surface of 

 the globe. But when the muscles relax, the fat resumes its original 

 place, and with it the cartilage also retires. 



THE CARTILAGO NICTITANS, WHEN REMOVED 

 FROM THE EYE OP A HORSE. 



DIAGRAM, TO ILLUSTRATE THE ACTION OF THE OABTILAOO NICTITANS UPON THE HORSE'S ETE. 



When any foreign body gets between the two layers of membrane, 

 instant winking results ; the gland, stimulated by the motion of the lid, 

 sends forth a gush of liquid. It is not simply a tear or two, but a 

 deluge of fluid is emitted; this flood, aided by the action of the lid, 



