366 SENSITIVE SYSTEM. 



pression of the eye : in general these wrinkles are more strongly 

 marked in old horses. The lids are separated by a transverse 

 aperture or slit, at the extremities of which they have angular 

 junctions denominated the cant/ii or angles of the eye: the su- 

 perior or temporal angle is sharp, is situated in respect to the 

 other in the direction of an oblique line drawn upward and in- 

 clined outward, and has a loose and moveable attachment to 

 the tarsal ligament ; the inferior angle is extended and rounded 

 off, and is firmly fixed to the tendon of the orbicularis. The 

 palpebral aperture exposes more or less of the eye in different 

 animals and individuals : in man and in the pig much of the 

 white of the eye is seen ; but in the horse and in quadrupeds in 

 general the transparent part only is exposed, unless when the 

 eye happens to be turned to one side. The extent of this open- 

 ing will likewise account for the impression made upon us that 

 one individual has a large or full eye, another a small or sunk 

 eye ; for I believe that the magnitude of the eyeball itself will 

 be found to vary but inconsiderably, or at least not sufficiently 

 to amount to this apparent diversity. The loose portion of in- 

 tegument entering injto the composition of the upper lid is a pro- 

 longation from the skin covering the forehead ; that of the lower 

 lid is derived from the face. Many short horse-hairs, but not 

 more than three or four long ones, are observable in the upper 

 lid, growing in the same direction as those upon the orbital 

 prominence above ; but from the lower lid stand erect six or 

 seven hairs of considerable length, without any regular arrange- 

 ment, which appears to be stationed there as sentinels to give the 

 alarm to the organ of approaching danger ; for, if by any acci- 

 dent one of them happen to be touched by an insect or any 

 foreign body, the lids are thrown, involuntarily, into a con- 

 vulsive twinkle with such alertness, as almost for a certainty to 

 shield the eyeball from impingement. The internal surfaces of 

 the lids are shaped into uniform concaves, to adapt them to the 

 globe of the eye, with which they are everywhere in close appo- 

 sition. They are lined by the conjunctive membrane. The 

 hems of the lids, the ciliari/ borders as they are called, are con- 

 siderably firmer and something thicker than the other parts, but 

 this augmentation of substance diminishes towards the temporal 

 angle : they limit our view of the eyeball, across which the 

 upper border swells into a curve, while the lower proceeds nearly 

 in a straight line. Each of these borders has two facings or 

 margins: the anterior margin is set with a row of horse-hairs, 

 denominated eyelashes ; the posterior is hairless and smooth, 

 broadens as it approaches the inferior canlluis, and slopes a 

 little inward in such manner, that, when the lids are closed, a 



