838 THE STOMACH. THE INTESTINE. 



The absorbents are very numerous; arising from a very fine superficial plexus 

 immediately underlying the tubular glands, they form a coarser deeply situated net- 

 work, between the areolar and muscular coats ; the vessels proceeding from this 

 network pierce the muscular coats, then follow the direction of the blood-vessels 

 beneath the peritoneal investment, and traverse lymphatic glands found along the 

 two curvatures of the stomach. No trace of lymphatics has been found between the 

 tubuli, therefore the whole depth of the secreting structure intervenes between the 

 layer of lymphatics and the contents of the stomach, whereas capillary blood-vessels 

 are distributed close to the surface ; an arrangement which seems favourable for the 

 interchange of material between the contents of the stomach and those of the blood- 

 vessels rather than of the lymphatics. 



The nerves, which are large, consist of the terminal branches of the two pneumo- 

 gastric nerves, belonging to the cerebro-spinal system, and of offsets from the sympa- 

 thetic system, derived from the solar plexus. Numerous small ganglia have been 

 found by Remak and others on both the pneumo-gastric and sympathetic twigs. The 

 nerves may be traced through the submucous coat, but no farther, as they then lose 

 their tubular character, and cannot be distinguished from other tissues. (Kolliker.) 

 The left pneumo-gastric nerve descends on the front, and the right upon the back of 

 the stomach. 



The pylorus. While there is no special apparatus at the cardiac orifice of 

 the stomach for closing the passage from the oesophagus, the opening at the 

 pyloric end, leading from the stomach into the duodenum, is provided with 

 a sphincter muscle. On looking into the pyloric end of the stomach, the 

 mucous membrane is seen projecting in the form of a circular fold, called 

 the pylorus, leaving a correspondingly narrow opening. Within this fold 

 are circular muscular fibres, belonging to the general system of circular 

 fibres of the alimentary canal, which are here accumulated in the form of 

 a strong band, whilst the longitudinal muscular fibres and the peritoneal 

 coat pass over the pyloric fold to the duodenum, and do not enter into its 

 formation. Externally the pylorus may be easily felt, like a thickened 

 ring, at the right end of the stomach. Internally its opening is usually 

 circular, and less than half an inch across, so that it is the narrowest part 

 of the whole alimentary canal. (See figures 581 and 586.) 



Occasionally the orifice is oval, and it is often placed a little to one side. Some- 

 times the circular rim is imperfect, and there are found instead two crescentic folds, 

 placed one above and the other below the passage (Huschke) ; and, lastly, there is 

 occasionally but one such crescentic fold. 



THE SMALL INTESTINE. 



The small intestine reaches from the pylorus to the ileo-csecal valve, at 

 which it opens into the large intestine. It consists of a convoluted tube, 

 measuring on an average about twenty feet in length in the healthy adult, 

 and becoming gradually slightly narrower from its upper to its lower end. 

 Its numerous convolutions occupy the middle regions of the abdomen, and 

 are surrounded by the large intestine. They are connected with the back 

 of the abdominal cavity, and are held in their position by a covering and 

 fold of the peritoneum, named the mesentery, and by numerous blood- 

 vessels and nerves. 



The small intestine is arbitrarily divided into three portions, which have 

 received different names ; the first ten or twelve inches immediately suc- 

 ceeding to the stomach, and comprehending the widest and most fixed part 

 of the tube, being called the duodenum, the upper two-fifths of the remainder 

 being named the jejunum, and the lower three-fifths the ileum. There 



