NORMAL HISTOLOGY. 



Additional minute lymphoid nodules and mucous glands occur 

 within the conjunctival fornix. The ocular conjunctiva pre- 

 sents no marked differences until near the corneal margin, where the 

 epithelium loses its columnar character and assumes the stratified 

 squamous type in its reflection over the cornea. 



The edge of the lid presents two borders, the outer, rounded off 

 and tegumental in character, and the inner, distinguished by its 

 sharply-defined margin and dense fibrous structure. In addition to 

 the orifices of the Meibomian glands, the palpebral border is pene- 

 trated by the ducts of the glands of Moll, structures properly 

 regarded as modified sweat-glands. 



The vertical fold of conjunctiva occupying the inner canthus, the 

 plica semilunaris, represents the third eyelid, or membrana 

 nictitans, of the lower animals. In exceptional cases the base of 

 the fold contains a minute plate of hyaline cartilage ; a small race- 

 mose gland, the homologue of the Harderian gland, is also some- 

 times present at the base of the semilunar fold. 



The lachrymal caruncle within the inner canthus is an isolated 

 and modified island of skin, possessing an epithelium, a corium, 

 and subcutaneous tissue similar to the adjacent integument ; the 

 epithelium, however, is without the stratum corneum. The caruncle 

 contains adipose tissue, fine hairs with relatively large hair-follicles, 

 and modified sweat-glands closely resembling the glands of Moll. 

 A small amount of involuntary muscle usually exists in the car- 

 uncle, and sometimes a few additional fibres of striped muscle. 



The blood-vessels of the eyelids pass from the outer and inner 

 angles towards the centre of the lid, forming an arch, the arcus 

 tarseus, along the edge of the lid, and a second anastomosis, the 

 arcus tarseus externus, at the upper margin of the tarsal plate ; 

 from these arterial bows smaller twigs are given off, which, in addition 

 to supplying the integument, the Meibomian glands, and the glands 

 of Moll, form the conjunctival capillary net-work ; additional branches 

 pass to the fornix conjunctivae and to the conjunctiva of the eyeball. 



The lymphatics of the lid are arranged as two sets : the close- 

 meshed conjunctival net-work within the tarsal mucous membrane, 

 and the wide-meshed peritarsal net- work on the front of the tarsus 

 at its upper border. The first set include the lymphatics running 

 near the palpebral border, as well as the narrow channels surrounding 

 the Meibomian glands. The conjunctival lymph- vessels communi- 

 cate with the peritarsal net-work by means of the coarse reticulum 

 within the tarsus surrounding its glands, as well as by direct connec- 

 tions established by the twigs which pierce the tarsus to join the 

 net-work within the conjunctiva. The peritarsal lymphatics possess 

 valves. 



