204 PHYSIOLOGY FOR BEGINNERS CHAP. 



muscles, and in addition by a small gland on the outer side 

 of the orbit called the lachrymal gland. This gland, 

 which is like a simple salivary gland in structure, secretes a 

 watery fluid, which when excessive escapes as tears. Usually 

 the fluid, which is always being formed, after flowing over the 

 eyeball, is collected by two canals, 

 the openings of which are readily 

 seen, one on the edge of each eyelid 

 c i ose to t he inner corner of the eye. 

 ' The two canals soon unite to form 



t ^ ie l ac hi"ymal duct, one for each 

 eye, which conducts the fluid to 

 the cavity of the nose. In addition 

 to the lachrymal secretion, which 



FIG. 94. Front view of left eye, i .> r r .v u 11 i 



1 keeps the front of the eyeball clean 



wrth eyelid partly removed to * * 



show lachrymal gland L.G, and <d moist, there is also a thicker 

 lachrymal duct L.D. fluid formed by small glands situ- 



ated in the eyelids. 



General Structure of the Eye. Obtain the eye of a 

 bullock from a butcher. Carefully clear away the fat at the 

 back of the eye so as to see distinctly the optic nerve, of which 

 there will probably be about half an inch left passing into the 

 eyeball. The fat will be surrounded by an almost continuous 

 sheath of muscle which is made up of the six distinct muscles 

 cut across in taking the eye out of the orbit. Hold the 

 eyeball carefully, and very gently squeeze it behind so as to 

 keep the front of it tense. You will see that the eyeball 

 is not a simple round globe, for the extreme front is raised and 

 more strongly curved than the rest, as if it were a piece of 

 a smaller globe put on to a larger one. This front part is 

 called the cornea. It is transparent, but appears dark 

 since dark internal structures are seen through it. It is con- 

 tinuous at its edge with the white thick fibrous outer coat of 

 the eyeball, the sclerotic. Just beyond the edge of the 

 cornfca you will be able to pick up a thin shining membrane 

 attached to the eyeball all round ; this is the conjunctiva. 



The eye of a man appears black in the centre, with a 

 variously -coloured ring round the centre. In bullocks' eyes 

 the centre is dark grey and is surrounded by a black ring. 

 The ring, variously coloured in ourselves and black in the 



