THE STOMACH. 



161 



The muscular coat, composed entirely of unstriped muscle, comprises 

 three irregular layers the external of longitudinal, the middle of circular 

 and the inner of oblique fibres. None of these layers is complete in all 

 parts of the stomach, the circular being the least imperfect and usually the 

 most conspicuous. The external layer consists of longitudinal fibres, con- 

 tinuous with the corresponding ones of the oesophagus above and with those 

 of the duodenum below. It is best developed along the lesser curvature, 

 over the greater curvature and intervening surfaces being a thin and irregular 

 stratum. Towards the pylorus the longitudinal fibres form a more compact 

 and thicker layer, which passes without interruption over the gastro-intestinal 

 junction into the outer mus- 

 cle of the duodenum. The 

 middle layer, while com- 

 plete and circularly dis- 

 posed within the pyloric 

 end, is imperfect and ob- 

 lique towards the fundus. 

 It is continuous above with 

 the superficial circular fibres 

 of the gullet; these, on 

 reaching the stomach, how- 

 ever, are arranged as loops, 

 which overlie the lesser 

 curvature but do not reach 

 the fundus. As these loops 

 pass downward they in- 

 crease in length and regu- 

 larity until, at the middle of 

 the stomach, the circular 

 strands completely girdle 

 the organ. Towards the 

 pylorus the circular bundles 

 thicken and, at the imme- 

 diate end of the stomach, 

 surround the opening into 

 the intestine with a robust 

 muscular ring, the pyloric 

 sphincter, the outer part of 



whirh alonp rnntirmp<; intn FIG. 200. Section of pyloric end of stomach, showing glands and 



part of a lymph-nodule. X 182. 



the duodenum, \nztnner 



layer, the least complete and most oblique, begins at the left of the cesopha- 

 geal orifice as a prolongation of the deeper circular fibres of the gullet. 

 On the stomach the fibres are disposed as loops which cover the fundus with 

 a fairly continuous layer, but become progressively more oblique and incom- 

 plete over the surfaces of the middle third, being absent over the lesser 

 curvature and the pyloric fourth of the stomach. It is evident, therefore, 

 that within the narrow tubular part of the organ, the muscle layers 

 have the most definite and orderly disposition; here they show in 

 cross-sections as a well-developed inner circular and a definite external 

 longitudinal stratum (Fig. 199). 



The serous coat corresponds in structure with other portions of the 

 visceral peritoneum, consisting of the surface mesothelial plates and the 

 subjacent tunica propria of fibro-elastic connective tissue. 



