476 Mr. C. B. Lockwood. Arteries of the Abdomen 



sidered first ; although, it may be remarked that a great- many of the 

 events which are about to be mentioned are in progress at the same 

 time. 



The position of the stomach is indicated by an enlargement of the 

 anterior portion of the mid-gut. This organ, like the remainder of 

 the bowel, is fastened to the spine by a mesentery, and simply hangs 

 suspended in the pleuro-peritoneal cavity (Diagram 1). This position 

 is altered by the stomach turning upon its right side. The mesentery, 

 or mesogastrium as it will be called in future, is implicated in this 

 change; instead of descending vertically from the spine to the 

 stomach, it becomes looped (Diagram 2). Owing to these movements 

 of the stomach and mesogastrium the cavity which they partitioned 

 becomes different. There is no longer a right and left division of the 

 peritoneal sac, but a part in front and to the left of the stomach and 

 mesogastrium, and a part behind and. to the right. The space which 

 is behind the stomach, and which has the mesogastrium for its left 

 boundary, represents what afterwards is the lesser cavity of the peri- 

 toneum. It need not be repeated that blood-vessels pass through the 

 mesogastrium to the stomach, and are of necessity involved in the 

 changes which have just been described. Their course, instead of 

 being straight, forms a curve. The relations of these altered vessels 

 to the subdivisions of the peritoneal cavity require to be noted ; it is 

 -evident that to reach their destination they now pass round the left 

 boundary of the future lesser sac. 



Diageam 2. 



S. Stomach. MG. Mesogastrium. 



All the changes which have been narrated occur at very early 

 stages of development ; subsequent events do not produce any great 

 alterations. Later it will be seen that the stomach becomes less 

 vertical, and its mesentery further modified ; but the changes which 

 the mesogastrium undergoes are very striking. They have been fully 



