447 



some segments, and longitudinally in others. The same condition ob- 

 tains in the outer layer. 



Between the preceding stage and that represented by a pig 23 cm 

 long (Fig. 7), there has been a general increase in the thickness and 

 differentiation of all the layers of the oesophagus. Their character, 

 however, remains, in general, the same. An important change, however, 

 is observed in the Submucosa, in the appearance of the oesophageal 



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Fig. 4. Cross section of the Oesophagus of a pig 11 cm long, at the level of the 

 bifurcation of the Trachea. Same preparation as Fig. 1. "^ 105. M Mucosa. MP 

 Basement membrane. 3IM Muscularis mucosae. SM Submucosa. IC Inner layer and 

 OL Outer layer of the Tunica miiscularis. 



glands. These begin as downgrowths of the epithelium of the mucosa 

 consisting of tubes lined by a double layer of low epithelium (Fig. 7, D). 

 Passing between the muscle bundles of the Muscularis mucosae, they 

 begin to branch and the alveoli (Fig. 7, A) are formed by the budlike 



