GENESIS OF NASOLACRIMAL PASSAGES IN MAN 9 



and in a brief time it has grown to such an extent that it reaches 

 into the underlying mesenchymal tissue. Witness for example 

 figs. 3 and 8, which represent frontal sections through the left 

 nasal fossa of an embryo aged approximately thirty-five days. 

 In these figures the ridge of epithelial cells has grown into the 

 underlying mesenchymal tissue. Note especially, however, that 

 the anlage still retains its connection with the rete mucosum 

 of the epidermis along the course of the naso-optic groove, in 

 which it has its genesis. Note further that the anlage is as yet 

 solid and that there is no evidence of lumen formation. 



Fig. 9 represents a semi-frontal section through a later stage of 

 the anlage (embryo aged about forty-three days). Note that 

 now the cord of epithelial cells is entirely detached from the sur- 

 face, i.e., it has entirely lost its connection with the rete mucosum 

 of the epidermis from which it arose. The anlage of the naso- 

 lacrimal passages now lies well embedded in the mesenchymal 

 tissue. It will be further noticed that the central cells of the 

 cord-like anlage (fig. 9) have taken the stain less deeply, and 

 apparently there is already an attempt at lumen formation. Some 

 of the central cells seem to be in a state of 'necrobiosis.' The 

 cells of the cord are apparently becoming re-arranged to form a 

 wall in anticipation of a later lumen. 



In the serial frontal sections through the nasal cavity of a 

 forty-three day embryo represented in figs. 10 and 11, the com- 

 plete isolation from the surface of the nasolacrimal passages at 

 this stage of development is well illustrated. The embryo from 

 which these photomicrographs were made is in a splendid state 

 of preservation. It is human embryo no. 3 (Hess Embryo) of 

 the Cornell University Series. It belongs to the research col- 

 lection of Professor and Mrs. Gage. 



This embryo shows several very important points in connec- 

 tion with the development of the nasolacrimal passages: In the 

 first place we find at this stage that the anlages of the nasolacri- 

 mal passages are nowhere connected with the epidermis, but that 

 they are entirely encompassed by mesenchymal tissue. In the 

 second place it will be noticed that the cords of cells are solid, 

 with here and there evidences of lumen formation. The series 



