VISION. * 331 



upper straight muscle of the eye-ball. The eye-lashes are 

 curved in opposite directions, so as not to interfere with 

 each other when the eye-lids are closed. Their utility in 

 guarding the eye against the entrance of various substances, 

 such as hairs, dust, or perspiration, and also in shading the 

 eye from too strong impressions of light, is sufiiciently ap- 

 parent. The eye-lids, in closing, meet first at the outer 

 corner of the eye; and their junction proceeds along the 

 line of their edges, towards the inner angles, till the contact 

 is complete: by this means the tears are carried onwards in 

 that direction and accumulated at the inner corner of the 

 eye, an effect which is promoted by the bevelling of the 

 margins of the eye-lids, which, when they meet, form a 

 channel for the fluid to pass in that manner. When they 

 arrive at the inner corner of the eye, the tears arc conveyed 

 away by two slender ducts, the orifices of which, called 

 the puncta lacrymalia (p, p,) are seen at the inner corner 

 of each eye-lid, and are separated by a round projecting 

 body (c,) connected with a fold of the conjunctiva, and 

 termed the lacryrnal caruncle. The two ducts soon unite 

 to form one passage, which opens into a sac (s,) situated at 

 the upper part of the sides of the nose, and terminating be- 

 low (at n) in the cavity of the nostrils, into which the tears 

 are ultimately conducted. When the secretion of the tears 

 is too abundant to be carried off by this channel, they over- 

 flow upon the cheeks; but when the quantity is not exces- 

 sive, the tendency to flow over the eye-lid is checked by an 

 oily secretion proceeding from a row of minute glands, si- 

 tuated at the edge of the eye-lids, and termed the Meibo- 

 mian glands. 



The eye-brows arc a fiU'ther protection to the eyes, the 

 direction of the hairs being such as to turn away from them 

 any drops of rain or of perspiration which may ciiancc to 

 fall from above. 



Excepting in front, where tlie eyes are covered and pro- 

 tected jjy the eye-lids, these important organs are on all 



