678 



THE EYE 



The scleral portion of the conjunctiva is nearly identical in structure 

 with the palpebral portion already described. Near the margin of the 

 cornea the superficial cells of the epithelium become at first spheroidal 

 and then, as the cornea is approached, they are progressively flattened, 

 so that, just outside of the corneal margin, the conjunctival epithelium 

 conforms to the stratified squamous type which forms the anterior epi- 

 thelium of the cornea. 



The blood supply of the eyelids is derived from the internal palpe- 

 bral artery which furnishes a branch to each lid; these two branches 



anastomose at the external angle 

 with the lacrimal branch of the 

 ophthalmic, through the external 

 palpebral artery. These trans- 

 verse ARTERIAL VESSELS (primary 

 tarsal arches) lie near the free 

 margin of the lids between the 

 tarsus and the orbicularis palpe- 

 brarum muscle. Each tarsal arch 

 sends pre-tarsal twigs forward to 

 supply the muscle and integu- 

 ment, and post-tarsal twigs back- 

 ward to supply the tarsal fascia, 

 the tarsal glands and the conjunc- 

 tiva. At the basal end of the tar- 

 sus, just back of the levator pal- 

 pebraB muscle, a second arch (the 

 (secondary tarsal arch) may be present, more commonly in the upper 

 lid; this second arch represents a larger branch of the palpebral artery, 

 and it anastomoses freely with the primary arch. The VEINS follow an 

 essentially similar course. The LYMPHATICS likewise include a pre- and 

 post-tarsal set, which unite to form larger tarsal tributaries which drain 

 along the facial vein toward the sub maxillary lymph nodes. 



The nerve supply includes sensory, motor and sympathetic fibers. 

 The main trunks lie between the tarsus and the orbicularis palpebrarum 

 muscle. The sympathetic fibers supply the blood-vessels, the smooth 

 muscle of Miiller, and the glands. Motor fibers contributed by the facial 

 nerve, supply the annular sheet of striped muscle; the oculomotor 

 nerve contributes motor fibers to the levator palpebrse muscle. The 

 sensory fibers, which are derived from the trigeminal nerve, end in naked 

 fibrils among the cells of the external integument and the internal con- 



FIG. 568. ARTERIAL SUPPLY OF THE EYE- 

 LID. 



(After Fox.) 



