832 THE STOMACH. 



At its cardiac orifice it is continuous with the oesophagus, and is, there- 

 fore, fixed to the cesophageal opening in the diaphragm. The pyloric ex- 

 tremity, situated lower down, nearer to the surface, and having greater 

 freedom of motion, is continuous with the duodenum. It is covered by the 

 concave surface of the liver, and in some cases touches the neck of the gall- 

 bladder. 



When the stomach is distended, its position and direction are changed. 

 The O3sophageal end, being fixed to the back part of the diaphragm, cannot 

 undergo any considerable change ; but the duodenal extremity has more 

 liberty of motion. The lesser curvature is, also, somewhat fixed to the 

 liver by the small omentum, while the great curvature is the most movable 

 part : accordingly, when the stomach is distended, this curvature is elevated 

 and at the same time carried forwards, whilst the anterior surface is turned 

 upwards, and the posterior surface downwards. 



Structure. The walls of the stomach consist of four distinct coats, held 

 together by fine areolar tissue. They are named, in order from without in- 

 wards, the serous, muscular, areolar or submucous, and mucous coats. By 

 some the areolar coat is not reckoned as a separate tunic. Taking all the 

 coats together, the walls of the stomach are thinner than those of the 

 oesophagus, but rather thicker than those of the intestines generally. 

 They are thickest at the pyloric end, and thinnest in the great cul-de- 

 sac. 



The external or serous coat, derived from the peritoneum, is a thin, 

 smooth, transparent, and elastic membrane which closely covers the entire 

 viscus, excepting along its two curvatures. Along the line of these curvatures 

 the attachment is looser, leaving an interval occupied by the larger blood- 

 vessels. 



The second or muscular coat is composed of three sets of unstriped fibres, 

 disposed in three layers, and named, from their direction, the longitudinal, 

 the circular, and the oblique fibres. 



The first or outermost layer consists of the longitudinal fibres, which are 

 in direct continuity with those of the oesophagus. They spread out in a 

 radiating manner from the cardiac orifice, and are found in greatest abun- 

 dance along the curvatures, especially on the lesser one. On the anterior 

 and posterior surfaces they are very thinly scattered, or are scarcely to be 

 found. Towards the pylorus they are arranged more closely together and 

 form a thicker uniform layer, which, passing over the pylorus, becomes con- 

 tinuous with the longitudinal fibres of the duodenum. 



The second set consists of the circular fibres, which form a complete layer 

 over the whole extent of the stomach. They commence by small and thinly 

 scattered rings at the left extremity of the great cul-de-sac, describe larger 

 and larger circles as they surround the body of the stomach concentric to its 

 curved axis, and towards the pyloric end again form smaller rings, and at 

 the same time become much thicker and stronger than at any other point. 

 At the pylorus itself, they are gathered into an annular bundle, which pro- 

 jects inwards into the cavity, and forms, together with areolar tissue and the 

 lining mucous membrane, the pyloric sphincter and valve. Some of the 

 circular fibres appear to be continued from those of the oesophagus, spreading 

 from its right side. According to Pettigrew the fibres of this layer are not, 

 as usually described, mere rings or circles, but rather double loops in the 

 form of the figure of eight, the two parts of which cross each other very 

 obliquely. 



The innermost muscular layer is incomplete, and consists of the oblique 



