1 86 THE ENGINES OF THE HUMAN BODY 



jected by a contraction wave escape into the duodenum. 

 We shall see that it is controlled by a most elaborate 

 mechanism. We notice, too, that while one wall or 

 border is short and runs straight from the cardiac to the 

 pyloric gateway, a distance of four or five inches, the other 

 is dilated or blown out so as to fill the left dome of the 

 diaphragm and make a sweeping curve as it passes from 

 one orifice to the other. It is plain that the stomach is 

 merely a dilatation or expansion of a simple muscular 

 tube, but it is not a uniform expansion ; the enlargement 

 affects only that side which forms the great curvature. 

 Hence we are prepared to find that its flaccid but stout 

 wall is made up, like that of the oesophagus, of two main 

 coverings or coats — a thick inner lining, studded with 

 minute chemical laboratories, and an outer muscular coat 

 concerned with the pulping and transport of the food. 

 The muscular coat is more intricate than that of the 

 oesophagus because it has several duties to carry out. 

 Its muscle spindles are grouped into three strata : in the 

 outer the spindles are directed lengthwise and can shorten 

 the chamber ; the inner is circular and can make it 

 narrow and long — it is the circular fibres which produce 

 the contraction rings we have just been witnessing ; the 

 middle stratum has its fibres arranged obliquely in an 

 intermediate direction. By the interaction of these three 

 strata the stomach can be emptied and its shape altered 

 according to requirements. In our drawing (fig. 40) no 

 representation has been given of structures of the utmost 

 importance — the arteries, veins, lymphatics, and nerves of 

 the stomach. The stomach is profusely supplied with 

 blood. Its lining membrane is flushed with a close- 

 meshed network of capillary vessels, with minute test-tube 

 glands — chemical retorts — stuck within the meshes of the 

 capillary field ; that field is fed by arteries which spring 

 straight from the aorta ; the blood from it drains into 

 veins leading to the liver. Nerves stream into both 

 lining and muscular coats from two sources : from nerve 

 or exchange centres in the medulla, and from others set 

 within the middle region of the spinal cord. There are 



