GLANDS 



219 



The Meibomian ylands, belonging to the group of sebaceous 

 glands, are confined to the Mammalia, and lie embedded in the 



FIG. 17oA. DIAGRAM TO ILLUSTRATE THE SHIFTING OF THE LACHRYMAL GLAND 



WHICH HAS TAKEN PLACE IN THE COURSE OF PHYLOGENY. 



The gland shifts in the direction of the arrows ; a, its position in the Amphibia ; 

 b, in Reptiles and Birds, and occasionally in Man, in which case it may be 

 regarded as atavistic ; c, normal position in Man. 



substance of the eyelids in the form of branched tree-like tubes 

 or clustered masses. They open on the free edge of the lid, and 

 produce a fatty secretion. Certain modified sweat-glands known as 



FIG. HOB. DIAGRAM OF THE LACHRYMAL APPARATUS OF MAN. 



TD, lachrymal gland, divided up into several portions ; **, ducts of the lachrymal 



fland ; tt, puncta lachrymalia ; TR, TR 1 , upper and lower lachrymal canals; 

 , lachrymal sac ; D, naso-lachrymal duct. 



the glands of Moll are also present immediately within the eyelids 

 of Mammals. 



The naso-lachrymal duct, which conducts the lachrymal 

 secretion into the nose, has already been referred to (p. 201). 



