248 THE ORGANS 



covered by ciliated cells. Bounding the stroma externally is a 

 strongly developed layer of longitudinal elastic fibres, the elastic 

 limiting layer, which separates the stroma from the muscular coat 

 and sends stout bands in between the muscle bundles of the latter. 



2. The muscular coat lies beneath the elastic layer and is 

 formed of very irregularly arranged muscle fibres belonging to the 

 constrictor muscles of the pharynx. 



3. The fibrous coat consists of a dense network of mixed fibrous 

 and elastic tissue. It has no distinct external Hmit, and binds the 

 pharynx to the surrounding structures. 



The distribution of blood-vessels, lymphatics, and nerves is 

 similar to that in the oral mucosa. 



Small, branched, tubular, mucous glands are present in the stroma, 

 and extend down into the intermuscular connective tissue. They 

 are most numerous near the opening of the Eustachian tube. 



TECHNIC 



For the study of the structure of the walls of the pharynx, material should 

 be prepared as in technic 2, p. 228. 



11. THE FOREGUT 



The (Esophagus 



viThe walls of the oesophagus are continuous with those of the phar- 

 ynx and closely resemble the latter in structure. They consist of 

 four layers, which from within outward are mucous, submucous, 

 muscular, and fibrous (Figs. 151 and 153). 



1. The mucous membrane resembles that of the pharynx except 

 that beneath the stroma is a well-developed muscularis miicosce com- 

 posed of smooth muscle cells arranged longitudinally. The muscu- 

 laris mucosae forms a complete coat only in the lower part of the 

 oesophagus. The epithehum is stratified squamous and rests upon 

 a papillated stroma . 



2. The submucosa is composed of loosely arranged fibrous and 

 elastic tissue. It contains mucous glands, the larger blood-vessels, 

 lymphatics, and nerves. 



3. The Muscular Coat. — In the upper portion of the oesophagus 

 this coat is composed of striated muscle fibres; in the middle portion, 

 of mixed striated and smooth muscle. In the lower portion there are 



