196 



HISTOLOGY. 



in case the intestinal tube is uncovered by peritonaeum, or the tunica 

 serosa if the peritonaeum is present. The following account of the subdi- 

 visions of the digestive tube is essentially a description of modifications in 

 these fundamental layers. 



OESOPHAGUS. 



The oesophagus is a tube about 9 inches long, the several layers of 

 which are continuous anteriorly with those of the pharynx, and posteriorly 

 with those of the stomach. It is lined with a stratified, many layered 

 epithelium like that of the pharynx. The free surface which is smooth 

 but thrown into coarse longitudinal folds, (Fig. 221) is covered with 



Stratified epithe- 

 lium. 



Tunica propria. 

 Muscularis 

 mucosae. 

 Submucosa. 



Mucous 

 membrane. 



Group of fat cell. 



cles. 

 Tunica adventitia. 



Mucous gland. 



Lymph nodule. 

 FIG. 221. TRANSVERSE SECTION OF THE UPPER THIRD OP THE HUMAN OESOPHAGUS. X 5. 



squamous cells; the basal surface is indented by papillae of the tunica pro- 

 pria. A muscularis mucosae, consisting of longitudinal smooth muscle 

 fibers, arises at the level of the cricoid cartilage and continues into the 

 stomach. At its anterior end it begins as scattered bundles inside the 

 elastic layer of the pharynx, and as the muscles increase to form a distinct 

 layer, the elastic lamina terminates. Beneath the muscularis mucosae 

 is the submucosa, containing the bodies of the oesophageal mucous glands. 

 They are tubulo-alveolar branched glands, with bodies about 2 mm. long, 

 and closely resemble those of the mouth. Crescents and serous cells are 

 absent, although empty cells may suggest the latter. Their ducts pass 



