88o 



ORGANS FOR THE PROTECTION OF THE EYE. 



punctum was overlooked by Toldt; Gerlach found an incomplete sphincter- 

 muscle. The canaliculi empty at separate points into a dilatation of the lacrimal 

 sac. The connective-tissue covering of the sac and the canal is united to the 

 neighboring periosteum. The thin mucous membrane, rich in lymphoid cells, 



has a double layer of (ciliated ?) 

 cylindrical epithelium, which 

 becomes stratified and squa- 

 mous below. The opening of 

 the canal is often provided 

 with a valve-like fold (Has- 

 ner's valve). 



The tears are con- 

 ducted between the lids 

 and the eyeball by capil- 

 larity, being distributed 

 evenly by the movements 

 of winking. The Meibo- 

 mian secretion prevents 

 the tears from overflowing 

 the lid-margins. The pas- 

 sage of the tears through 

 the puncta, the canaliculus 

 and the canal is effected 

 largely by siphonage, but 

 this is assisted materially 

 by Homer's muscle 

 (known also to Duvernoy 

 in 1678), which , with every, 

 act of winking, draws the 

 posterior wall of the sac 

 backward, dilating the sac, 

 and thus exerting an aspir- 

 atory influence on the 

 tears. Scimemi has demon- 

 strated this experimen- 

 tally by introducing a 

 fine tube through the wall 

 into the lumen of the 

 lacrimal sac (in human 

 beings with lacrimal 

 fistula) : fluid is aspirated 

 in this tube with every 

 closure of the lids. 



E. H. Weber and v. Has- 

 ner believe that the tears are 

 aspirated by rarefaction of 

 the air in the nasal cavities 

 in the act of inspiration and 

 in that of insufflation. Arlt 

 thinks the sac is compressed 

 by _ the contraction of the 

 orbicularis, so that the tears 



FIG. 



Lid 



corum; B and 



.Vertical 



ieyer): A, cutis; i, epidermis; ., ^unum, D ana 7 

 subcutaneous connective tissue; C and 7, obicularis muscle, 

 with its bundles; Z>, loose, submuscular connective tis- 

 sue; E, insertion of Heinrich Miiller's muscle- F tarsus' 

 Cr, C9njunctiva; /, inner lid-margin; k, outer lid-margin-' 

 4, Pigment-cells, in the cutis; 5, sweat-glands; 6, hair- 

 follicles with hairs; 8 and 23, cross-section of nerves; 9, 

 arteries; 10, veins; u, aha; 12, modified sweat-glands 

 ^'n? ary usd S''- J 4' orifice of a Meibomian 



1, 15, cross-section of its acini; 16, posterior tarsal 

 glands, 18 and 19, tissue of the tarsus; 20, pretarsal or 

 submuscular connective tissue; 2I and 22 conjunctiva 

 with its epithelium; 24, adipose tissue; loose-meshed 

 posterior extremity of the tarsus; 26, section of a palpe- 





must escape toward the nose, 

 illy, Stellwag believes that 



-j -~ ^L the lids; while according 



tor pumping the tears into the lacrimo-nasal canal exists. 

 lowever, to one point, namely that the tissue surrounding 



