THE SPLEEN IN MONOTREMES. 



Platypus (Ornithorhynchus anatinus.) 



On opening" the abdomen of the Platypus, concomit- 

 ant with the presence of a diaphragm and great omentum 

 one is struck by the large development of the spleen and 

 pancreatic tissue, and the right stem of the former may 

 extend from the left hypochondrium to the right iliac 

 region. 



The spleen (p. 136) is somewhat V-shaped, and three 

 portions are recognised, viz., a small body 2.5 to 3 cm. 

 long directed towards the oesophagus and in the great 

 omentum (lesser sac) ; a large right ventral (anterior) 

 process lying freely in the abdominal cavity and sus- 

 pended also in the great omentum, 12 to 15.5 cm. long, 

 with the width varying from 2 to 2.5 cm. and thickness 1.5 

 cm. ; and a shorter left dorsal (posterior) process 7 to 9 

 cm. long, with a width of 1.75 to 2 cm. and thickness of 

 nearly 1 cm. This left process is outside the lesser sac in 

 relation with a fold — the left lateral or lieno-mesocolic- 

 connecting it to the mesocolon of the left or distal colon. 

 The distal colon is never fixed dorsally, and the average 

 maximum width of the mesocolon equals 5 cm. The pan- 

 creas is found diffusing itself on the left aspect of the 

 mesocolon in relation with the left lateral fold. The fold 

 with the left splenic process and pancreas can be lifted 

 free from the ventrum of the left kidney and the dorsal 

 wall. Whilst the right process and body of the spleen are 

 continuous, the left process is arched and forms practi- 

 cally a right angle with the body. A deep notch is present 



135 



