These conditions mostly result from obstruction to the passage of food through the pylorus from contraction of that orifice. A simple weakness of the muscular coat may also allow of passive distension. Obstruction of the pylorus, causing an accumulation of the contents, leads in the first instance to a simple distension of the organ, which tells chiefly on the parts which are free to swell out. The lesser curvature is fixed by its attachments, and it usually retains nearly its normal position except that its middle part is somewhat dragged downwards. The greater curvature, on the other hand, is carried downwards, and the stomach may virtually fill the entire abdomen, reaching as far as the symphysis pubis in some cases. Sometimes the pylorus is depressed and the duodenum correspondingly displaced.

The general result of obstruction of an orifice is compensatory hypertrophy of the muscular coat of the viscus, such as frequently develops in the heart and urinary bladder. But the muscular coat of the stomach has a somewhat different function to that of the heart or bladder. In the latter there is a simultaneous contraction of the entire muscle with a view to the emptying of the viscus. In the stomach, however, the contraction is vermicular, and its object is as much to move the contents about inside the stomach as to empty them into the duodenum. In the actual propulsion of the contents into the duodenum it is the pyloric portion of the stomach that is engaged, and here also the material is carried forward by a vermicular movement. Hence the hypertrophy of the muscular coat in obstruction of the pylorus does not occur uniformly in the stomach, but localizes itself in the pyloric portion, sometimes even with a special thickening just at the orifice, forming a tight Sphincter. In these cases, when the wall of the stomach is divided, the progressive thickening of the rigid muscular coat can often be distinguished as the pylorus is approached. As the muscle of the stomach is in bundles, hypertrophy produces an exaggeration of these, and on section they are frequently very prominent, especially as the connective tissue septa between them are also hypertrophied. The alternative bundles, as seen on section, have been compared with the leaves of a fan.

Besides general dilatation, which is of common occurrence, a localized dilatation or Diverticulum is met with, but is exceedingly rare. Tilger describes a case of Traction-diverticulum (see under (Esophagus) in which the traction from without of an adherent and displaced gall-bladder had been the cause. Pulsion-diverticula are equally rare. In the case illustrated by Fig. 389, the diverticulum was essentially a hernia of the mucous membrane through the muscular coat and was thus comparable with the much more common "false diverticula" of the intestine.

Literature

Penzoldt, Magenerweiterung, 1875; Leube, in Ziemssen's Encycl., vii., 1877; Tilger, Virch. Arch., cxxxiii., p. 201, 1393; Joshua Ferguson, (Diverticula) Glas. Med. Jour., 1897 (with references).