444 



of cells, there is a distinct basement membrane, which stains deeply 

 with aniline blue and is in intimate connection with the fibrils of the 

 adjacent connective tissue. The latter is much more differentiated 

 than in the younger stages as the fibrils are denser and are present 

 in relatively greater quantity. The cellular elements of the syncitium 

 possess less cytoplasm and do not anastomose so freely. Some distance 

 from the embryonic mucosa, there is a denser mass of cells in the 

 syncitium, the direction of which is chiefly circular. These may be 

 said to represent the anläge of the Tunica muscularis (Fig. 1, IC). 

 There can be no difleren- 

 tiation of the layer further, 

 although, here and there, 

 a few cells are seen in 

 cross section outside of 

 the circularly directed 



Fig. 1. Fig. 2. 



Fig. 1. Section of the Oesophagus of a 13 mm pig, fixed in Zenker's P'luid and 

 stained with Malloey's Aniline blue-Fuchsin-Orange G Mixture. X 1^^- ^^ Mucosa. 

 MP Basement membrane. S3I Submucosa. IC Anlage of the Tunica muscularis. 



Fig. 2. Cross section of the oesophagus of a 3 cm pig at the level of the bifur- 

 cation of the trachea. Same preparation as Fig. 1. ^ 105. 31 Mucosa. 3IP Base- 

 ment membrane. Sßl Submucosa. IC Inner layer of the Tunica muscularis. OL Outer 

 layer of the Tunica muscularis. 



fibres. As yet, there is no evidence of the presence of the Muscularis 

 mucosae. We may say, then, that the oesophagus, at this period, 

 consists of the embryonic Mucosa, made up of a stratified columnar 

 epithelium, the Submucosa, and the Tunica muscularis, simple and poorly 

 differentiated though they may be. 



In a pig 3 cm long, the oesophagus (Fig. 2) has not lost its oval 

 form, but the mucosa begins to show the infoldings so characteristic 

 of the organ in the adult. Its lumen is now in the form of a Greek 

 cross, yielding four somewhat irregular longitudinal folds, which pro- 

 ject into the lumen of the organ. This invagination involves the 



