1888.] ANATOMY OF THE LACERTILIA. 99 



case from the Society's collection. The points which I have par- 

 ticularly studied are two : — (1) the bile-ducts, which are curiously 

 complicated in Varanus, (2) the relations of the peritoneum to the 

 enclosed viscera. In respect of both these points the Varanidee differ 

 very strikingly from all other Lacertilia ; but as the number of 

 genera which I have been able to investigate is small, I can at present 

 only put forward tentatively a suggested emendation in the current 

 schemes of classification of the Lacertilia. 



1. Peritoneum. 



In Iguana the body-cavity is a spacious pleuroperitoneal cavity 

 lined by peritoneum, which, as in Lacerta, is deeply pigmented 

 posteriorly ; this cavity is partially divided into two, right and left, 

 halves by the umbilical ligament (fig. 1); the heart is surrounded 

 by a special serous sac, the pericardium ; beyond this there is no 

 subdivision of the body-cavity. It is commonly stated that the 

 diaphragm is unrepresented in the Lacertilia; the attachment of the 

 pericardium to the parietes may, however, as has been suggested, be 

 an indication of such a structure. 



In Monitor (fig. 2) there is some little difference ; when the body- 

 walls are cut open and reflected, the alimentary viscera are not exposed 

 as they are in Iguana. A loose membrane covers these viscera ; the 

 membrane looks as if it were simply the lining peritoneum of the 

 abdominal cavity which had got separated and detached from the 

 abdominal parietes ; this is, however, not the case ; an examination 

 by the aid of the microscope showed clearly that a layer of peritoneum 

 covers the abdominal musculature, and is quite distinct from the 

 horizontal membrane ; in Varanus griseus the peritoneal layer was 

 particularly distinct, for the reason that it contained numerous 

 pigmented corpuscles. For the greater part this membrane is free 

 from the ventral parietes ; anteriorly it is attached to the median 

 ventral line ; dorsally it is attached along the spinal column ; here 

 and there it is also attached to the lateral parietes by membranous 

 bands. It passes over the lobes of the liver and the stomach, and 

 shuts off the lungs from the abdominal cavity. The umbilical 

 ligament dividing the two liver-lobes is present as in Iguana, and is 

 attached to the dorsal side of the horizontal membrane. This 

 horizontal membrane also separates the kidneys from the reproduc- 

 tive glands ; the latter lie internally to it ; the kidneys are placed 

 outside it. The ventral surface of this membrane bears a vein of 

 some size, the anterior abdominal vein. The fat-body when present 

 lies below the membrane, and is therefore shut off from the abdominal 

 cavity. 



I found this membrane present, with the general arrangement that 

 has been above stated, in 



Monitor gouldi. 



Monitor bengalensis. 



Varanus salvator. 



Varanus niloticus. 



Varanus griseus. 



