PLATYPUS AND ECHIDNA. 



trace is seen in Tas. Devil) from the dorsum of 

 duodenal pancreas to the inf. v. cava. But in the Echidna 

 the definition of gastro-hep. omentum (lesser omentum) 

 is distinct. The pancreas becomes attached by a peri- 

 toneal fold to the lobus caudatus, and this fold is really 

 continuous with one to the inf. v. cava (which is present), 

 so that the latter fold from pancreas to v. cava seen in 

 Platypus is the starting point in the fixation of duodenum 

 and pancreas. As a result, what may be regarded as a 

 twist is put on the "junction'' of the lesser omentum and 

 mesoduodenum, and the former becomes denned, forming 

 the anterior boundary of the foramen of Winslowii. In 

 the Platypus this, as stated, was a gap on the right of 

 gastro-hep. omentum and mesoduodenum, which were 

 practically continuous. In only one Echidna did the 

 condition resemble that of the Platypus, and here there 

 was no attachment of pancreas to caudate. This throws 

 light on formation of foramen Winslowii, and shows why 

 we go behind lesser omentum to enter the lesser sac. 

 Light is also thrown on the mobility of the caudate lobe- 

 after fixation of pancreas, then immobility; but mobile 

 first to give a yield to the band, and the pancreas itself, 

 when evolving, is diffuse and mobile. Why fixed duo- 

 denum and pancreas? For erect posture, i.e., no mobility 

 of ducts allowed, thus obviating torsion. 



Portal Vein. — On the right side a single branc'i 

 passes, sending branches, one to right lateral, and another 

 to the caudate and spigelian lobes. On the left side two 

 branches are given off close together — one to left lateral 

 lobe, and the smaller to the left mesial lobe. The branch 

 to the right mesial would appear to be a continuation of 

 the portal trunk. 



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