j6o NORMAL HISTOLOGY. 



their course within the submucous tissue, and send off branches to 

 supply the mucosa in a similar manner as in the mouth. The lym- 

 phatics are exceptionally numerous in the vicinity of the lymph- 

 follicles, around which they form net-works continuous with those 

 of the nasal cavity, the oesophagus, and the larynx. 



The nerves supplying the pharynx, derived from the cranial and 

 sympathetic trunks taking part in the formation of the pharyngeal 

 plexus, contain both medullated and non-medullated fibres, associ- 

 ated with minute ganglia. Small twigs are given off from the larger 

 branches to terminate in the subepithelial tissue and among the acini 

 of the mucous glands and the lymphatic follicles. 



The walls of the digestive tract, from the oesophagus to the anus, 

 are composed of four tunics the mucous, the submucous, the 

 muscular, and the fibrous or serous. The muscular coat, 

 usually thickest and most rigid, is the most essential structure in 

 maintaining the form of the tube. The mucosa is distinguished 

 by the highly-specialized secreting apparatus which it contains, as 

 well as by the variations and the modifications of its surface ; 

 the difference between the several divisions of the digestive tract is 

 dependent largely upon the changes in the character of this tunic. 



The submucosa loosely connects the mucous coat with the mus- 

 cular, and affords space for the larger blood-vessels, the lymphatics, 

 and the nerves, as well as for some few glandular structures and 

 lymphoid masses. 



The fibrous coat gives additional strength to the walls of the 

 digestive tube, and presents a smooth external serous surface in those 

 parts of the tract which receive a reflection from the peritoneum. 



THE CESOPHAGUS. 



The walls of the oesophagus comprise four coats the mucous, 

 the submucous, the muscular, and the fibrous. 



The mucous membrane is a continuation of that of the pharynx, 

 and corresponds closely with the latter in structure. 



The stratified squamous epithelium rests upon the connective- 

 tissue matrix, the tunica propria, the inner surface of which bears 

 numerous small papillae completely hidden by the thick overlying 

 epithelium. The deeper layers of the mucosa are separated from 

 the submucous coat by longitudinal bundles of involuntary muscle, 

 the muscularis mucosae ; these muscular bundles, absent in the 

 upper part of the oesophagus, first appear as irregular and inter- 

 rupted groups, which become more numerous until, from the middle 

 of the tube on, they form a continuous longitudinally-disposed layer. 



The submucous coat is composed of loosely-united connective 

 tissue, serving for the conveyance and support of the larger blood- 



