THE DIGESTIVE TRACT. 



161 



vessels, lymphatics, and nerves. Within the submucosa are placed 

 likewise the acini of the mucous glands; these are rather more 

 numerous on the anterior surface, their ducts piercing the mucosa 

 and opening on the free surface of the mucous membrane, being 

 lined throughout the greater part of their length by columnar epi- 

 thelium. In the lower portion of the oesophagus, particularly about 



FIG. 195. 





Section of human oesophagus : a, squamous epithelium of surface resting upon fibrous tissue of 

 mucosa, the deeper part of which is occupied by muscularis mucosae (6) ; c, submucous coat, con- 

 taining glands (h); d, e, respectively circular and longitudinal muscular tunics; e 1 ', e', bundles of 

 striped muscle-fibres. 



the cardiac orifice, the mucous glands are very plentiful and lie 

 within the mucosa. 



The muscular tunic consists of two layers, an inner circular 

 and an outer longitudinal, whose component bundles are held 

 together by the connective-tissue septa which pass between the fas- 

 ciculi in all directions. The character of the muscular tissue varies 

 in the several portions of the tube. That contained within the wall 

 of the upper third of the oesophagus is entirely of the striated 

 variety, while the muscular tissue of the lower third is exclusively 







