416 



ELEMENTARY PHYSIOLOGY 



The upper eyelid is raised by a special muscle, the 

 levator of the upper lid, which arises at the back of 

 the orbit and runs forwards to end in the lid. 



The lower lid has no special depressor. 



At the edge of the eyelids the integument becomes 

 continuous with a delicate, vascular and highly nervous 

 mucous membrane, the conjunctiva, which lines the in- 

 terior of the lids and the front of the eyeball, its epithelial 

 layer being even continued over the cornea. The nume- 

 rous small ducts of a 



\1'":;aV>.\ 



S.Oi. 



gland which is lodged in 

 the orbit, on the outer 

 side of the ball (Fig. 1.33, 

 L.G.\ the lachrymal 

 gland, constantly pour 

 its watery secretion into 

 • the interspace between 

 the conjunctiva lining the 

 upper eyelid and that 

 covering the ball. On 

 the inner side of the 

 eye is a reddish fold, 

 the carunciala lachry- 

 malis, a sort of rudi- 

 ment of that third eye- 

 lid which is to be found 

 in many animals. Above 

 and below, close to the 



caruncula, the edge of each eyelid presents a minute 

 aperture (the pnndvm lachri/male), the opening of a small 

 canal. The canals from above and below converge and 

 open into the lachrymal sac ; the upper blind end of 

 a duct {L.D., Fig. 134) which passes down from the orbit 

 to the nose, opening below the inferior turbinal bone 

 (Fig. 69, h). It is through this system of canals that the 

 conjunctival mucous membrane is continuous with that 

 of the nose ; and it is by them that the secretion of the 



rn/!06. 



Fia. 133. 



The front view of the right eye 

 dissected to show Orb. the orbicular 

 muscle of the eyelids ; the pulley 

 and insertion of the superior oblique, 

 S.Ob., and the inferior oblique 

 Inf. Ob. ; L.G, the lachrymal gland. 



