449 



We have thus briefly traced all of the organogenetic processes of 

 the oesophagus from the simplest form until the appearance of all of 

 the characteristics of the adult organ are present. It will be observed 

 that the ciliated epithelium described in the human oesophagus does 

 not occur at this level 

 in the organ of the pig. 

 The consideration of this 

 point together with the 

 later history of the 

 oesophagus will appear 

 in another place. 



We may say, then, 

 by way of resume that 

 the organogenesis of the 

 oesophagus in the lower 

 segment about the level 

 of the forking of the 

 Trachea, takes place in 

 the following way: 



1. The Mucosa is 

 derived from the simple 

 epithelium of the head 

 gut, which, in the early 

 embryos, consists of a 

 single or double layer 

 of cubical or columnar 

 epithelium. After the 

 saparation of the trachea 

 and oesophagus from the 

 head gut is practically 

 complete, as in an em- 

 bryo 6 mm in length, 

 the primitive is oval in 

 form and is lined by a 

 layer of epithelium com- 

 posed of two rows of 

 columnar cells. In still 

 later stages, the character 

 of the epithelium remains 

 the same, but the number of layers increases. Then, the inner row of 

 cells loses its columnar character gradually until it is replaced by one 











Fig. 6. Cross section of the Oesophagus of a pig 

 21,5 cm long taken at the level of the bifurcation of the 

 Trachea. X 1^5. M Mucosa. MP Basement membrane. 

 SM Submucosa. MM Museularis mucosae. IV Inner 

 layer and OL Outer layer of the Tunica museularis. 



Anat. Anz. Aufsätze. XXX. 



29 



