224 DISEASE IN WILD MAMMALS AND BIRDS 
certain infectious diseases like enterohepatitis and amoe- 
biasis, the cystic and extreme right lobes are more affected 
than the left parts of the organ. In the bird tliis is not 
so difficult to follow since the three divisions of the portal 
vein, while they combine at times in an ampulla within the 
hilum of the liver, seem directed to certain lobes, that 
from the left portal seeming to point toward the right 
side. The avian portal system differs from the mammalian 
in having a large branch from the renal area, the so-called 
renal-portal system, pass to the liver, and by having a 
free anastomosis between the portal area and the caudal 
vena cava whereby blood from the pelvic district may 
pass into the general circulation without going through 
the liver. There is no unanimity of opinion as to the func- 
tion or importance of this connection (2) and from 
the data collected here there is no peculiar reno- 
hepatic pathology. 
The gall-bladder is not a constant organ in either mam- 
mals or birds and indeed it may be absent or present in 
very closely related species (Two-toed Sloth present. 
Three-toed Sloth absent). When present in mammals it 
is usually a dependent bag while in birds it commonly lies 
upon the cystohepatic duct, between the liver and the 
last curve of the duodenum, in some varieties filling from 
the bottom, the inlet being guarded by a valve. This 
cystic duct in nearly all birds, comes exclusively from the 
right lobe while the hepatic duct, with which the cystic 
has no connection, is formed by combination within the 
liver of radicles from both sides. It passes to the duo- 
denum well in advance of the cystic duct, in some birds, 
e.g., the Struthiones, very near the pylorus, that is on 
the descending limb of the duodenal loop. By this means 
obstruction to the biliary stream is rendered difficult. The 
common duct combines with one of the pancreatic outlets 
in most mammals but the abdominal salivary gland in 
(2) See Woodland, Proc. London Zool. Soc, 1906, and MacLeod, 
Chemical and Physiological Medicine, Chicago, 1923. 
