478 Mr. C. B« Lockwood. Arteries of the Abdomen 



omentum than of the stomach, yet it does not seem unreasonable to 

 argue that they represent the original vessels of the mesentery. 



If the course of the gastric artery, through the mesogastrium, has 

 been followed, that of the splenic offers fewer difficulties. Exactly 

 similar principles of development apply to it. 



If the mesogastrium of a human embryo about 2 inches long be 

 examined the following facts may be easily observed. Near the 

 oesophagus the mesogastrium is comparatively short, but at the 

 j auction of the anterior with the middle third of the stomach it is 

 longer, and the rudiment of a spleen may be distinguished between 

 its layers. This organ is developed from the mesoblast which exists 

 between the layers of the mesogastrium. It will be remembered that 

 a portion of this tissue had previously become differentiated into the 

 blood-vessels of the mesogastrium. Whether the spleen and its blood 

 supply are formed at the same time and from the same tissue, or 

 whether this .organ appropriates some of the vessels which the 

 mesogastrium previously contained, would be hard to say. The fact 

 remains that the mesoblast from which this organ is developed is 

 in direct continuity, behind, with that which surrounds the aorta, in 

 front, with that which forms the wall of the stomach ; there is no 

 anatomical reason, therefore, why either of the above events might not 

 occur. As soon as the spleen appears blood-vessels can be seen 

 extending to it from the aorta, and onwards to the stomach. Entirely 

 situated between the layers of the mesogastrium the spleen derives 

 the whole of its blood supply from vessels passing through it. At 

 the period at which the spleen is formed the mesogastrium has become 

 involved in the change of position which the stomach undergoes. 

 Owing to the turning of this organ upon its right side, the meso- 

 gastrium forms B: fold the convexity of which is towards the left. 

 The portion of the general peritoneal cavity included in the concavity 

 of the fold represents the lesser sac. Now the spleen appears at the 

 convexity of the loop, so that the portion of mesogastrium which extends 

 from the spine to the spleen forms the left boundary of the lesser cavity, 

 and that which passes from the spleen to the stomach constitutes the 

 gastrosplenic omentum (Diagram 3). The application of these facts 

 to the course of the splenic artery is not difficult. As this vessel runs 

 in the mesogastrium it ought to commence behind the lesser peritoneal 

 sac, and pass in its left boundary to reach the spleen. It is also clear 

 that a portion of the greater cavity, that which lies between the 

 posterior surface of the mesogastrium and back wall of the abdomen, 

 should be behind the artery. That this is so may easily be ascertained 

 by examining a human foetus at about the full term. At this period 

 the mesogastrium is well marked, and the splenic artery plainly 

 between its layers. Even in the adult there is a well marked recess, 

 so that, by placing one hand in the lesser sac and another behind the 



