250 THE ORGANS 



profusely. Some contain both chief and acid cells, others only chief 

 cells (see stomach, page 254). They lie in the tunica propria, and are 

 for the most part confined to a narrow zone at the lower end of the 

 oesophagus and to the level of the fifth tracheal ring. Scattered 

 groups also occur in other regions. 



The distribution of blood-vessels, lymphatics, and nerves in the 

 oesophagus is similar to their distribution in the mouth (p. 227). Be- 

 tween the two muscular coats the nerve fibres form plexuses in which 

 are many sympathetic nerve cells. These plexuses are analogous to 

 the plexuses of Meissner in the stomach and intestine. 4 



TECHNIC 



Remove a portion of the wall of the oesophagus, wash carefully in normal 

 salt solution, and pin out, mucous-membrane side up, on a piece of cork. Fix in 

 formalin-Miiller's fluid and harden in alcohol (technic 6, p. 7). Transverse or 

 longitudinal sections should be cut through the entire thickness of the wall. If 

 the details of the muscular coat are to be studied, sections from at least three 

 different levels should be taken: one near the upper end, one at about the 

 middle, and the other in the lower third. Stain with haematoxyUn-eosin or 

 haematoxylin-picro-acid-fuchsin (technic i, p. 20; 3, p. 21) and mount in balsam. 



General Structure of the Walls of the Gastro-intestinal 



Canal 



^The walls of the stomach and intestines are made up of four coats 

 (Fig. 152). These from the lumen outward are mucous, submucous, 

 muscular, and serous. 



I. The mucous membrane (Fig. 152) consists of surface epithe- 

 lium, glands, stroma, and muscularis mucosas. The surface epithe- 

 lium is simple columnar and rests upon a distinct basement membrane. 

 The arrangement of the glands and the nature of the gland cells differ 

 in different parts of the tract. The stroma is a loosely arranged, 

 richly cellular connective tissue, which in many places is so infiltrated 

 with lymphoid cells as to constitute diffuse lymphatic tissue. In 

 other places it contains circumscribed masses of lymphatic tissue, 

 lymph nodules. The amount of stroma depends upon the closeness 

 with which the glands are packed. The muscularis mucosce consists 

 of smooth muscle cells, which have a generally longitudinal arrange- 

 ment. Where, however, the muscularis mucosae is thick there are 

 usually two distinct layers — an inner circular and an outer longitudi- 



