445 



Mucosa and Submucosa alone as the Tunica muscularis does not 

 partake in the process and retains its oval form. At the same time, 

 there are slight changes observable in the character of the Mucosa, 

 consisting chiefly in a decrease in the definiteness of the columnar 

 character of the inner row of cells next to the lumen of the oeso- 

 phagus. Their contours are no longer so sharp and the protoplasm 

 is much clearer. The changes in the Submucosa consist, other than 

 in an increase in its size, in a strengthening of the fibrils forming the 

 framework which now stain more deeply and are present in relatively 

 greater quantity than the cells. 



The Tunica muscularis is now more sharply differentiated and 

 may be readily divided into two distinct layers (Fig. 2, 2C, OL). The 

 course of the fibres 

 in the outer and 

 inner strata of muscle 

 is not longitudinal 

 and circular respec- 

 tively, as the bundles 

 of muscle fibres seem 

 to interlace so that 

 the course in both 

 sheets is, in one place, 

 circular and, in an- 

 other, longitudinal. 

 The muscle cells are 

 spindle shaped with 

 no evidence of sar- 

 costyles or striations 

 in cross or longi- 

 tudinal sections. At 

 this stage, the Mus- 

 cularis mucosae can- 

 not be recognized as 

 such. Small nerves 

 and ganglia derived 

 from the Nervus va- 

 gus, are seen at many 

 points growing into 

 the muscle layers. 



In the next stage, i. e. a pig 7,5 cm long (Fig. 3), there are few 

 changes to record outside of the definite appearance of the Muscularis 





Fig. 3. Cross section of the Oesophagus of a pig 7,5 cm 

 long at the level of the bifurcation of the Trachea. Same 

 preparation as Fig. 1. X 1^5. M Mucosa. M3I Muscularis 

 mucosae. S3I Submucosa. IC Tunica muscularis. 



