850 



THE INTESTINE. 



run immediately beneath the serous tunic; many pierce the muscular coat, sup- 

 plying it with vessels as they pass, and having entered the submucous areolar 



Fig. 596. Fig. 596. ENLARGED VIEW 



OF ONE OF BRUNNER'S 

 GLANDS FROM THE HUMAN 

 DUODENUM (from Frey). 



The main duct is seen 

 superiorly ; its branches are 

 elsewhere hidden by the 

 bunches of opaque glandular 

 vesicles. 



layer, ramify in it, so as to 

 form a close network, from 

 which still smaller vessels 

 pass on into the mucous 

 coat, and terminate in the 

 capillary network of the 

 folds, villi, and glands of 

 that membrane, which is 

 the most vascular of all 

 the intestinal tissues. The 

 fine capillaries of the mus- 

 cular coat are arranged in two layers of oblong meshes, which accompany and cor- 

 respond in direction with the longitudinal and circular muscular fibres. The veins 

 accompany the arteries. 



The absorbents of the intestine may be conveniently distinguished as those of the 

 mucous membrane and those of the muscular walls. Those of the mucous mem- 

 brane form a copious plexus which pervades both the mucous and submucous layers, 

 the largest vessels being those which are in the latter layer ; but there is not, in the 

 human subject at least, the same distinct division into two strata which has been 

 found in the stomach (Teichmann). With regard to the absorbents of the muscular 

 walls, it has been stated in a former part of this work (p. 491) that, according to the 

 concurrent accounts of the various investigators of this subject, the absorbents of the 

 intestine are in two strata, viz., those of the submucous layer already mentioned, 

 and a subserous set, following principally a longitudinal direction beneath the peri- 

 toneum, and having only an interrupted communication with the other through 

 intervening trunks ; but more recently, a paper by Auerbach has appeared, in which 

 it is stated as the result of transparent injections, that the only truly subperitoneal 

 plexus which exists is confined to a strip in the immediate neighbourhood of the 

 mesentery ; that the longitudinal plexus seen by previous observers is really situated 

 between the circular and longitudinal muscular coats ; and that, besides this, there 

 are likewise copious and close minute capillary plexuses, threading the whole thick- 

 ness of the muscular walls, in complete continuity with the mucous absorbents, and 

 throwing their contents into those larger vessels the position of which had been mis- 

 understood. To the whole of this series of absorbents Auerbach gives the name of 

 " interlaminar plexus." (Virchow's Archiv., vol. xxxiii., p. 340.) 



The nerves of the small intestine are chiefly derived from the superior mesenteric 

 plexus (see p. 702). This plexus is formed superiorly by nervous branches, of which 

 those in the middle come from the coeliac plexus, and the lateral ones proceed directly 

 from the semilunar ganglion. The plexus and plexiform branches into which it 

 divides cling at first very closely to the larger divisions of the superior mesenteric 

 artery, especially on their anterior surface, and, dividing similarly with the ramifi- 

 cations of the arteries, the branches of the nerves, retaining still a wide plexiform 

 arrangement, pass onwards to the different parts of the intestine between the two 

 folds of the mesentery, and finally, separating somewhat from the blood-vessels, reach 

 the intestine in very numerous branches. 



In regard to the nervous distribution in the coats of the intestine, two recent dis- 

 coveries of considerable interest have been made. One of them, for which we are 

 indebted to Auerbach, consists in the observation of a peculiar nervous plexus, rich 



