198 HISTOLOGY. 



they are not generally considered mucous cells, it has been found that in the 

 stomach their protoplasm responds to concentrated mucin stains, and it is 

 quite possible that they produce a variety of mucin. Occasionally the 

 oesophageal cardiac glands possess a few parietal cells like those found in 

 the stomach. Cystic enlargements and dilated ducts occur, as shown in 

 Fig. 222. No special function has been assigned to the cardiac glands. 



Beneath the submucosa is the tunica muscularis, consisting of an 

 inner layer of circular or oblique fibers, and an outer layer of longitudinal 

 fibers. In the anterior or upper part of the oesophagus the longitudinal 

 fibers predominate. The muscles there are chiefly striated and are con- 

 tinuous with those of the pharynx. Gradually they are replaced by 

 smooth fibers so that the striated forms are infrequent in the lower half of 

 the oesophagus. As its lower end the circular fiber layer is said to be three 

 times as thick as the longitudinal. The oesophageal muscles are joined by 

 slips from the trachea, left bronchus, aorta, and other adjacent structures. 



Outside of the muscularis is the connective tissue adventitia. It con- 

 tains branches of the sympathetic nerves and the oesophageal plexus of the 

 vagus nerves. From these, the nerves invade the muscularis forming 

 the ganglionated myenteric plexus between its 'layers, and pass on into 

 the submucosa where they constitute a poorly developed submucous plexus. 

 The terminal branches include free sensory endings in the stratified epi- 

 thelium, motor plates on the striated muscles and the simpler motor end- 

 ings on the smooth muscle. The blood vessels form capillary networks with 

 meshes between and parallel with the muscle fibers. They also branch 

 irregularly in the submucosa, and form terminal loops in the papillae 

 of the tunica propria. Lymphatic vessels are numerous. 



STOMACH. 



The inner surface of the stomach presents macroscopic longitudinal 

 folds which become coarse and prominent as the organ contracts. There 

 are also polygonal areas from i to 4.5 mm. in extent, bounded by shallow 

 depressions under which the gastric glands have been said to be fewer and 

 shorter than elsewhere. The depressions are also ascribed to the contrac- 

 tion of the muscles in the mucous membrane. Toward the pylorus, or 

 duodenal end of the stomach, there are small leaf-like elevations of the 

 mucous membrane, called plicae -villosae. They may connect with one 

 another to form a network. The gastric mucosa is pinkish gray since its 

 epithelium is thin enough to transmit the color of the blood beneath; this 

 is not true of the oesophagus, the lining of which appears white. 



The epithelium of the stomach is simple and columnar, the transition 

 from the stratified epithelium of the oesophagus being abrupt (Fig. 222). 



