THE EYE. 401 



sensibility, is ranked by Bichat among the mucous membranes. 

 It has, however, some peculiarities in its structure, for it is en- 

 tirely deficient in villosities, and though most abundantly fur- 

 nished with capillary vessels, they do not obviously admit red 

 blood, but in a state of irritation. *j 



Glandules Palpebrarum. These bodies also called the glands 

 of Meibomius, from an anatomist who has described them par- 

 ticularly, are situated at the margin of each eyelid, between its 

 cartilage and the conjunctiva. They are about two or three 

 lines long, and appear like small, white, serpentine threads, run- 

 ning at right angles to the margin of the lid, near to, and paral- 

 lel with one another. They are more abundant on the upper 

 than on the lower lid. They terminate by a row of small ori- 

 fices in the margin of the lid, just behind the cilia. For prevent- 

 ing the overflowing of the tears, and the sticking together of the 

 eyelids, they discharge an unctuous fluid, which may be made 

 manifest by squeezing them. Their secretion is occasionally 

 much augmented, and then has a large quantity of serum and 

 glutinous matter in it: in this case the evaporation of the se- 

 rum makes it adhesive, and causes the eyelids to adhere after 

 they have been closed for some time, as in sleep, 



Muscles. 



The Musculus Levator Palpebras Superioris is placed in the 

 superior part of the orbit. It arises by a small round tendon- 

 from the upper margin of the optic foramen, and, becoming 

 fleshy, it expands itself into a long thin triangle* of which the 

 base is in front. It covers the rectus superior muscle. 



Terminating in front by a thin tendinous expansion, it is in- 

 serted into the superior margin of the upper palpebral cartilage; 

 but some of its fibres continue on between the latter and the or- 

 bicularis to the lower edge of the cartilage. 



It raises the upper lid, by drawing it towards the bottom of 

 the orbit- 

 There are six muscles concerned in moving the eyeball 1 , four 

 of which, from their direction,, are said to be straight; and the; 



35* 



