184 



PHYSIOLOGY 



CHAP. 



able to take nourishment of all kinds in frequent, though not 

 abundant meals. 



IX. While the stomach is, in virtue of its glands, a digesting 

 organ, it is from its muscular coats an organ of special movements, 

 which serve in the first place to churn up the iugesta and bring 

 them into contact with the gastric juice, and in the second place, 

 to propel the semi-digested chyme onwards into the duodenum. 



Beneath the external serous coat the stomach has three 

 layers of plain muscular tissue. These are (from the direction of 

 their fibres) the longitudinal (outer), the circular (middle), and 

 the oblique (inner). The longitudinal fibres are directly con- 

 tinuous with those of the oesophagus; they radiate from the 



FIG. 59. A, section through pyloric ]>art of stomach and commencement of duodenum, from 

 specimen hardened in situ. (J. Symington.) a, a, a, longitudinal folds of mucous membrane in 

 pyloric part of stomach ; b, section of mucous membrane ; c, circular muscular fibres of 

 stomach ; the longitudinal fibres are just visible to the naked eye as a narrow line internal to 

 the circular fibres ; D, duodenum ; P, pyloric orifice. B, diagrammatic view in perspective of 

 portion of coats of stomach and duodenum, including pylorus. (Allen Thomson.) g, inner 

 surface of gastric mucous membrane; g', section of mucous membrane with pyloric gastric 

 glands ; v, villous surface of mucous membrane of duodenum ; i, section of same with crypts 

 of Lieberkiihn ; p, p, ridge of pyloric ring, with section of its component parts ; mi, circular 

 layer of muscular fibres, seen in the section to form pyloric sphincter; me, longitudinal 

 layer of muscular fibres ; s, serous covering. 



cardiac orifice, are more abundant along the curvatures, and thinly 

 scattered over the remaining surface of the stomach as far as the 

 pylorus, where they form a thick uniform layer, which passes over 

 the pylorus and becomes continuous with the longitudinal fibres 

 of the duodenum. The circular fibres form a close and complete 

 layer over the whole of the stomach. At the pyloric end they 

 become much thicker, and at the pylorus itself they form a 

 bundle within a circular fold of the mucous membrane, known as 

 the pyloric sphincter. Lastly, the oblique fibres are continuous 

 with the circular fibres of the gullet on the left of the cardiac 

 orifice, where they form a considerable stratum ; from this point 

 they descend obliquely, and spread out in different directions 

 upon the anterior and posterior surfaces of the stomach ; they 

 disappear at the pyloric antrum, mingling with the circular fibres 

 which predominate there (Fig. 59). 



In proportion as the stomach fills with food, it dilates, and 



