THE SPLEEN IX MARSUPIALS. 



cess is less closely attached than the body. The short, 

 wide left dorsal process is outside the lesser sac, being con- 

 nected to the mesocolon of the distal colon by the triangu- 

 lar fold, the left lateral or lieno-mesocolic, which is more 

 developed in some specimens than in others. It is free 

 from the dorsal wall and ventrum of the left kidney. Both 

 as regards its shape and the disposition of the left lateral 

 fold, the spleen of the Macropod presents the primitive 

 Mammalian type, and resembles closely that of the Mono- 

 treme. 



True Phalangers (Trichosurus — Pseudochirus) , 



In Trichosurus a marked advance towards the 

 human type of spleen is to be noted, and light is thrown on 

 the formation of the lieno-renal ligament and the mode 

 of fixation of the distal colon and spleen. Although three 

 portions of the spleen are noted, viz., body, right, and 

 short left processes, the organ is more compact and the 

 processes less defined than in the preceding mammals 

 (page 116). The body is directed towards the oesophagus 

 and is suspended — like the right ventral process, which is 

 directed along the great curvature of the stomach — on the 

 great omentum, i.e., lesser sac. 



The width of the great omentum (gastro-splenic) at 

 the extremity of the body is 1.5 cm., and at the extremity 

 of the right process the width is 5.5 cm., so that the nar- 

 rowing gastro-splenic omentum is here well defined. The 

 short left dorsal process is outside the lesser sac in rela- 

 tion with the left lateral fold. Its average length is only 

 1.5 to 2 cm. The total average length of the spleen is 

 7 cm. and the width 1.5 to 2 cm. In addition to the outer 

 or left and inner visceral or right surfaces, three margins 

 can be defined, viz., renal or dorsal margin formed by 

 the body and left process; right ventral margin formed 

 by the body and right process; and left colic margin 



143 



