GENESIS OF NASOLACRIMAL PASSAGES IN MAN 3 



of the nasolacrimal passages. He investigated this field in am- 

 phibia and found a structure homologous with that described 

 by Coste for mammals, but he found that its genesis did not agree 

 with Coste's hypothesis. 



Since Born's conception of the genesis of the nasolacrimal pas- 

 sages in amphibia applies also, broadly speaking, in other forms, 

 it may not be amiss to briefly quote his own words: 



Der Thranencanal der Amphibien bildet sich clurch Einwachsung 

 und Abschniirung ernes Epithelstreifens von der Nase bis zum Auge 

 hin der dann ein Lumen bekommt und sich mit der Nasenhohle in 

 Yerbindung setzt. 



While the above did not clear up the origin of the lacrimal 

 ducts in mammals, it nevertheless proved to be the correct inter- 

 pretation of the genesis of the main portion of the nasolacrimal 

 duct in all investigated forms up to the present. According to 

 Born, in amphibia, a solid strand of epithelial cells, extending 

 from the eye to the nose, becomes detached from the surface 

 epithelium and this strand of cells later acquires a lumen. The 

 strand of cells retains connections with the surface epithelium 

 at both the ocular and nasal ends. This strand of cells becomes 

 both the lacrimal ducts and the whole of the nasolacrimal duct. 



Born later (78) investigated lizards and birds and found that 

 the basic principles concerning the anlage of the nasolacrimal 

 passages in these forms agreed with what he found in amphibia. 

 He, however, found that the cord of cells differentiated along 

 the course of the oculo-nasal furrow; also that it differed somewhat 

 in its further development In both forms (lizards and birds) 

 a solid cord of cells became isolated from the surface. In lizards 

 the isolation was complete, i.e., there remained no connection 

 with the surface epithelium at any point; both lacrimal ducts 

 and the nasal end of the nasolacrimal duct developed as sprouts 

 from the mother cord of cells. As in amphibia the lumina of 

 these several channels were established later In birds the cord 

 of cells retained connection with the surface epithelium at both 

 the ocular and nasal ends. One of the lacrimal ducts, however, 

 developed as a sprout from the ocular end of the mother cord of 

 cells. 



