THE SPLEEN IN MARSUPIALS. 



(1) Mesial fold, approximating the colon to the 

 pyloric region, and continuous in the Chameleon with the 

 gastro-hepatie omentum or ventral mesogaster. 



(2) Duodenal or right lateral, passing from the 

 ascending duodenum to the right aspect of the mesocolon 



of the distal colon, which I regard as an acquired or phy- 

 siological fold (zygosis). 



(3) Left lateral or Iieno-mesocolic, from the left, 

 dorsal, or posterior process of the spleen to the left aspect 

 of the mesocolon of the distal colon. The mesial fold is best 

 defined in the Koala, the duodenal in Trichosurus, and 

 the lieno-mesocolic fold in the Platypus and Dasyures. 

 The origin of the left lateral or lieno-mesocolic fold was 

 certainly very puzzling, and at first I was inclined to 

 regard it as an acquired or physiological adhesion (zy- 

 gosis) from a spleen which had wholly developed in 

 relation to the lesser sac. A study of certain lizards 

 supplied me, however, with a different explanation (page 

 154). 



In Agama we notice the narrow splenic body in the 

 mesogaster running parallel with the stomach. In Lygo- 

 soma (Scincidae) the spleen was noticed passing almost 

 vertically close to the dorsal wall and in relation not only 

 with the mesogaster but with the mesentery and meso- 

 colon as well. Correlated with the development of the 

 Mammalian spleen we have the development of great 

 omentum, and, in the case of the Agama, the enlargement 

 would be wholly related to the lesser sac, as actually 

 happens in Koala, in which the left process is insignifi- 

 cant : while in the case of Lygosoma an enlargement of the 

 spleen would involve not only the mesogaster (great 

 omentum, lesser sac) but the mesocolon as well. In 

 Lygosoma the pancreas is noted as a single strand ex- 

 tending from the commencement of the duodenum to the 



15*2 



