268 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



splenic artery is one of the vessels of the inesogastrium (Fig. 219), 

 its branches end in the developing tissues of the spleen. The 

 splenic blood spaces are probably formed from the veins which in 

 the developing spleen are lined by a layer of columnar cells. 

 The trabecular and muscular tissue and the capsule are derived 

 from the mesoblast of the dorsal mesogastrium. 



The gastro-splenic omentum is that part of the dorsal meso- 

 gastrium which unites the spleen to the stomach (Figs. 216 and 

 217). It becomes elongated and stretched as the stomach rotates. 



left kidney - 

 spleen - 



gastro-sp/._ 

 oment 



storn.- 



gastro-hep. 



oment. 



jm 



■ right kidney 



-peritoneal cavity 



-aorta 

 -lieno-renal lig. 



■ splenic artery 



-liver 



-falciform lig. (vent, mesent.) 



Fig. 217.— A diagrammatic transverse Section of the Mesogastrium viewed from behind. 



The spleen comes to lie against the posterior (right) surface of the 

 cardiac end of the stomach. The dorsal part of the mesogastrium 

 between the roof of the coelom and the spleen becomes the lieno- 

 renal ligament. The rotation of the stomach also leads to the 

 spleen being thrust towards the left side ; the upper or renal 

 surface of the spleen becomes applied to the peritoneum covering 

 the anterior surface of the left kidney (Fig. 217). The part of 

 the mesogastrium between the spleen and oesophagus adheres to 

 the diaphragm and forms the suspensory ligament of the spleen. 

 The Pancreas. — The Pancreas appears during the 4th week as 

 two, or perhaps three, processes of hypoblast from that part of 

 the gut which afterwards becomes the second stage of • the 



