DIGESTIVE SYSTEM. 251 



exceeds his in weight and bulk by eight times, will not hold 

 more than three gallons, or four times the quantity of the man's. 

 We are to bear in mind, however, that the stomach, like other 

 hollow muscles, has the power of accommodating itself to the 

 bulk of its contained matters ; so that we are not at liberty to 

 draw conclusions of its comparative volume barely from the state 

 of plentitude in which we may find it. At another time I shall 

 endeavour to shew why Nature has given so small a stomach to 

 the horse ; an animal whose consumption of food we know to be 

 enormous. 



Structure. — The stomach is composed of four layers of sub- 

 stance, termed coats. The first is that which it derives from the 

 peritoneum, thence called the peritoneal coat : at the greater 

 curvature the layers coming from the omentum disunite and 

 separate, and spread uniformly over both surfaces of the organ. 

 In texture, this coat is the same as the parietal portion of the 

 membrane, and, like that, exhales a serous vapour from its sur- 

 face, to obviate friction between the stomach and those viscera 

 with which it lies in contact. Inwardly, the peritoneal adheres, 

 by a fine dense cellular tissue, to the next tunic. 



The second or muscular coat, lies immediately underneath the 

 peritoneal. It is composed of two orders of fibres, which may 

 be most plainly seen when the stomach is distended with air, and 

 its peritoneal covering stripped off. The exterior fibres run in 

 a longitudinal direction, and are fewer in number and weaker 

 than the interior, which take a circular course, and are strong 

 and well-marked, particularly about the pyloric extremity, where 

 they appear to be blended with those of the duodenum : from 

 this arrangement of the fibres, the cavity can be diminished in 

 every dimension*. If we slit open the pylorus, we shall find a 

 valvular projection, forming the boundary line, internally, be- 

 tween the stomach and the intestine : this is called the valve of 

 the pylorus; it is made up of a circular production of muscular 

 fibres enveloped within a fold of the internal coat. Though this 

 valve certainly tends to prevent the return of alimentary matter 

 from the intestines, yet do physiologists not regard this as its 

 principal use. They believe that its operation is rather that of 



* In a case of oedema of the coats of the stomach, I found the muscular 

 coat in a state particularly favourable for demonstration. I could not 

 detect any longitudinal fibres but at the curmttures ; and they were most 

 distinguishable around and in the vicinity of the great curvature. The 

 circular fibres were everywhere very strong and demonstrable — their 

 fasciculi were plainly shewn, in consequence of being separated and ele- 

 vated from the internal tunic by the serous fluid with which the connecting 

 cellular substance had become infiltrated. They were, many of them, nearly 

 as large as crow-quills, and put on a very pale ash-coloured hue. 



