120 HEAD AND NECK 



are flat, and that in each case the eyelashes project from 

 the anterior border, whilst the tarsal glands open along the 

 posterior border, a distinct interval intervening between the 

 cilia and the mouths of the glands. On the other hand, 

 the small portion of the margin of each eyelid which bounds 

 the lacus lacrimalis is more horizontal in direction, somewhat 

 rounded, and destitute both of eyelashes and of tarsal glands. 

 At the very point where the eyelashes in each eyelid cease, 

 and the palpebral margin becomes rounded, a minute emi- 

 nence with a central perforation will be seen. The eminence 

 is the papilla lacrimalis^ whilst the perforation, called the 

 punctum lacrimale, is the mouth of the lacrimal duct, which 

 conveys away the tears. Endeavour to pass a bristle into 

 each of the orifices. The upper duct at first ascends, whilst 

 the lower one descends, and then both run horizontally to the 

 lacrimal sac. 



The conjunctiva is the membrane which lines the deep 

 surfaces of the lids, and is reflected from them on to the 

 anterior aspect of the eyeball. At the margins of the lids it 

 is continuous with the skin, whilst, through the puncta lacri- 

 malia and the lacrimal ducts, it becomes continuous with 

 the lining membrane of the lacrimal sac. The line of re- 

 flection of the conjunctiva from the lids on to the eyeball is 

 termed the fornix conjunctives. Owing to the greater depth of 

 the upper lid, the conjunctival recess between the upper lid 

 and the eyeball is of greater extent than that of the lower lid. 

 The conjunctiva is loosely connected with the eyelids on the 

 one hand, and with the sclera of the eyeball on the other. 

 Over the cornea the membrane becomes thinned down to a 

 mere epithelial covering, which is closely adherent. 



In connection with the conjunctiva, the plica semilunaris 

 and the caruncula lacrimalis must be examined. The 

 caruncula is the reddish fleshy-looking elevation which 

 occupies the centre of the lacus lacrimalis. From its surface 

 a few minute hairs project. The plica semilunaris is of interest 

 because in the human eye it is the rudimentary representative 

 of the membrana nictitans, or third eyelid, found in many 

 animals. It is a small vertical fold of conjunctiva, which is 

 placed immediately to the lateral side of the caruncula, and it 

 slightly overlaps the eyeball at this point. 



Dissection. Distend the eyelids slightly by placing a little tow or cotton 

 wool steeped in preservative solution in the conjunctival sac ; then stitch 



