448 THE ALIMENTARY CANAL [CH. XXVII. 



THE STOMACH 



The stomach is a dilatation of the alimentary canal placed between 

 and continuous with the oesophagus, which enters its larger or cardiac 

 end on the one hand, and the small intestine, which commences at 

 its narrowed end or pylorus, on the other. 



Its wall is composed of four coats, (1) an external or peritoneal, 

 (2) muscular, (3) submucous, and (4) mucous coat ; with blood-vessels, 

 lymphatics, and nerves distributed in and between them. 



(1) The peritoneal coat has the structure of serous membranes in 

 general. (2) The muscular coat consists of three separate layers or 

 sets of fibres, which, according to their several directions, are named 

 the longitudinal, circular, and oblique. The longitudinal set are the 

 most superficial : they are continuous with the longitudinal fibres of 

 the oesophagus, and spread out in a diverging manner over the cardiac 

 end and sides of the stomach. They extend as far as the pylorus, 

 being especially distinct at the lesser or upper curvature of the stomach, 

 along which they pass in several strong bands. The next set, the 

 circular or transverse fibres, are most abundant at the middle and in 

 the pyloric portion of the organ, and form the chief part of the thick 

 projecting ring of the pylorus. They are continuous with the circu- 

 lar layer of the intestine. The deepest set of fibres are the oblique, 

 continuous with the circular muscular fibres of the oesophagus : they 

 are comparatively few in number, and are found only at the cardiac 

 portion of the stomach; they form a sphincter around the cardiac 

 orifice. The muscular fibres of the stomach and of the intestinal 

 canal are unstriated, being composed of elongated, spindle-shaped 

 fibre-cells. 



(3) The submucous coat consists of loose areolar tissue, which 

 connects the muscular coat to the mucous membrane. It contains 

 blood-vessels and nerves ; in the contracted state of the stomach it is 

 thrown into numerous, chiefly longitudinal, folds or rugae, which dis- 

 appear when the organ is distended. 



(4) The mucous membrane is composed of a corium of fine con- 

 nective tissue, which approaches closely in structure to adenoid 

 tissue ; this tissue supports the tubular glands of which the super- 

 ficial and chief part of the mucous membrane is composed, and pass- 

 ing up between them assists in binding them together. The glands 

 are separated from the rest of the mucous membrane by a very fine 

 homogeneous basement membrane. The corium is covered with a 

 layer of columnar epithelium, which passes down into the mouths of 

 the glands. 



At the deepest part of the mucous membrane are two thin layers 

 (circular and longitudinal) of unstriped muscular fibres, called the 

 muscularis mucosce. 



