7»6 A MANUAL OF ANATOMY 



i'and the vessels issuing from this plexus on entering the submucous 

 coat form another plexus, the lymphatics of which are furnished 

 with valves. The vessels which emerge from this latter plexus 

 accompany the bloodvessels, and pass to the small and great 

 curvatures, and the vicinity of the hilum of the spleen. At the 

 curvatures they are connected with the superior and inferior gastric 

 lymphatic glands, whilst those which accompany the vasa brevia 

 arteries pass through the splenic glands, the efferent vessels of all 

 these glands ultimately passing to the coeliac glands. In addition 

 to the lymphatic vessels just described there is a subperitoneal 

 lymphatic plexus. 



Nerves. — ^These are derived from (i) the two pneumogastric 

 nerves, and (2) sympathetic plexuses from the solar plexus. The 

 right pneumogastric nerve descends upon the posterior surface of 

 the stomach, whilst the left nerve descends upon the anterior surface. 

 The sympathetic -plexuses closely accompany the arteries. The 

 nerves form two gangliated plexuses composed of non-medullated 

 nerve-fibres. One of these is situated between the longitudinal and 

 circular fibres of the external muscular coat, and corresponds to 

 the plexus myentericus of Auerbach of the intestine. The other 

 plexus is situated in the submucous coat, and corresponds to the 

 plexus of Meissner of the intestine. 



. The explanation of the right pneumogastric nerve descending upon the 

 posterior surface, and the left upon the anterior surface, of the stomach is found 

 in the position assumed by the stomach in the early embryo. Briefly stated, 

 at that period of life the stomach is a straight tube, and its surfaces are right 

 and left. The two pneumogastric nerves, therefore, right and left, naturally 

 descend on the right and left surfaces of the viscus. When, however, the 

 stomach turns over on its right side, the surface which was originally right 

 becomes posterior, and the surface which was originally left becomes anterior. 

 Thus the right nerve eventually descends on the posterior (originally the right) 

 .•surface, and the left nerve descends on the anterior (originally the left) sur- 

 face. 



Pylorus. — ^The opening between the pyloric end of the stomach 

 and the duodenum is provided with a sphincter muscle, called the 

 sphincter Pylori, This is formed by an aggregation of the circular 

 muscular fibres, which causes the mucous membrane to project in 

 the form of an annular fold, thus giving rise to the pyloric valve. 

 The sphincter pylori is only relaxed when the contents of the 

 stomach are being passed into the duodenum. At all other times, 

 it is in a condition of firm contraction, and the pyloric orifice then 

 takes the form of a cleft. 



The. average length of the stomach is about 12 inches, and its average 

 width at the widest part about 5 inches. I t weighs about 4J ounces, and 

 its capacity, which is very variable, ranges from 3 to 5 pints. 



