202 ANSWERS TO PRACTICAL QUESTIONS 



lachrymal ducts. Finally, it allows a brief but periodical rest 

 to the levator muscle of the upper eyelid. MARSHALL. 



2(>. When you wink, do the eyelids touch at once along 

 their ivhole length ? Why ? 



In winking, both lids move, but the upper one much the 

 more extensively. Moreover, they do not come in contact all 

 along their margins at the same instant of time, but meet first 

 at the outer corner, and then rapidly inward as far as the 

 lachrymal papillae, on which the lachrymal ducts are situated. 

 By this sweeping movement, all foreign bodies are carried to 

 the lachrymal lake. MARSHALL. 



27. How many roivs of hairs are there in the eye- 

 lashes ? 



The eyelashes, or cilia, consist of two, and opposite the 

 middle of the eyelid, of three rows of finely-curved hairs 

 those of the upper lid being more numerous, thicker, and 

 longer than those of the lower lid. "Those of the upper lid 

 are curved upward, those of the lower lid are curved down- 

 ward; and when the lids are brought near together, these two 

 ranges of hairs stand like so many crossed sabers, or a kind of 

 chevaux-de-frise, guarding the entrance to the eye." D ALTON'S 

 Physiology, p. 330. 



28. Do all nations have eyes of the same shape ? 



No. Witness the almond-shaped eyes of the Chinese. 

 "The greater or less extent of the opening of the lids makes 

 the eye appear larger or smaller; the conformation of the pal- 

 pebral muscles and the tarsal cartilages gives to the eye an 

 elongated and languishing form, as in the East, or round and 

 bold, as among the Occidentals ; but the dimensions and form 

 of the globe are the same in all countries and in all individu- 

 als." Wonders of the Human Body. 



29. IVJiy does snuff-taking cause a floiv of tears ? 



Because of the action of the sympathetic system. 



