10 LYMPHATICS IN THE STOMACH OF THE EMBRYO PIG. 



dip down into the stomach wall and, as the muscular layers are traversed, the plexus 

 between the muscular layers is formed . This plexus extends throughout the stomach 

 wall, but its vessels are of smaller caliber and its meshes much less dense than those 

 of the other plexuses. It should be borne in mind, however, that vessels lying in 

 dense, muscular tissue fill less readily with injection mass than those situated in the 

 loose tissues of the submucosa and subserosa; therefore, the appearance of the 

 muscular plexus may be less dense than it really is. This point considered, the small 

 size of the vessels composing the plexus of the muscularis and their striking constancy 

 of arrangement in all well injected specimens nevertheless are facts which tend to 

 show that this plexus is a relatively scanty one. 



On reaching the submucosa these vessels form the most extensive plexus of 

 the stomach wall, the main plexus of the submucosa. Here lymphatic growth 

 takes place very rapidly. At an early stage (20 to 40 mm.) an extremely dense 

 plexus, several layers in thickness, composed of large, tortuous vessels, has been 

 formed. In embryos 70 to 100 mm. in length the entire submucosa is found to be 

 filled by this plexus. Its presence can be easily demonstrated throughout the 

 entire stomach by injecting directly into the submucosa. As it nears the pylorus 

 its vessels become smaller and many of them appear to end blindly in this region ; 

 however, a few of them have been seen to anastomose with those of the deep plexus 

 of the duodenum. In view of the general tendency toward anastomosis exhibited 

 by the lymphatics of contiguous tissue, which is especially marked in the lymphatics 

 of the subserous plexuses of the stomach and duodenum, this scanty connection 

 between the submucosal plexuses of these two organs can scarcely be considered as 

 representing the true morphology of the lymphatics in this region. It is evident 

 that the layers of the stomach wall at the pylorus are compressed by the tone of the 

 pyloric musculature, as are also the lymphatic channels of the submucosa. Such a 

 barrier proves quite effective in preventing complete injection of the vessels of this 

 region. The character of the apparent endings of the vessels of the submucosa at 

 the pylorus favors such a view. Instead of forming a complete plexus at this 

 point, most of the vessels end blindly and at different points along the pylorus, thus 

 giving the exact picture of an incomplete lymphatic injection elsewhere in the body. 

 From the injections we are justified in saying only that the pathway between the 

 submucous plexuses of the stomach and duodenum is not easily traversable during 

 tonic contraction of the pylorus. A sufficient number of anastomoses between 

 these two plexuses has been demonstrated to show that they are connected and, by 

 analogy to the lymphatics of the rest of the gastro-intestinal tract, one would expect 

 ready communication between them during relaxation of the pyloric sphincter. 



The further growth of the lymphatics in the wall of the stomach takes place 

 from this dense submucosal plexus. Many smaller vessels grow still farther inward 

 and form the scanty plexus adjacent to the muscularis mucosse. This plexus lies 

 at the base of the gastric glands and sends branches between them. 



Figure 8, plate 3, is from a complete injection of the stomach of a pig measuring 

 150 mm. It has been cut along the greater curvature and spread out to show 

 especially well the marked esophageal ring of lymphatics. This ring constitutes 



