THE LIVER 225 
lower animals has more often patent separate ducts or 
multiple ducts than it does in man. Birds have one to 
four pancreatic ducts separate from the biliary openings. 
The gall-bladder is missing in most varieties of the 
following groups: pigeons, parrots, wrens, ostriches, 
rheas, cuckoos, toucans among the birds; most odd-toed 
ungulates, hyraces, Indian elephants, all deer, peccaries, 
three-toed sloth, and many rodents. The varieties lack- 
ing this reservoir are herbivorous in the main, true 
carnivores seeming always to be possessed of such a 
structure. Among the important herbivorous ungulates, 
Bovidae, Tragulidae, Camelidae and Suidae have this bile 
reservoir almost mthout exception. Because of the 
interest now being shown in the pathology of the gall- 
bladder and its passages and of the pancreas, it was hoped 
that evidence of definite practical value for human pa- 
thology would be at hand in our study if we divided the 
animals into groups with and without a bile reservoir. 
The result is not unequivocal but worthy of note; it is 
discussed on pages 238 and 255. 
Microscopically the well known lobular arrangement 
of the liver is rather faithfully carried out among the 
mammals albeit the most systematic and complete archi- 
tecture is to be found in the pig while the marsupial seems 
the most disorderly, thus resembling the avian organ. In 
the latter class all the parts are indistinct, the cells having 
an unclear outline, the tubules being intricately wound 
and the interlobular connective tissue being scanty and 
not anastomosing in a definite framework. The intra- 
lobular reticulum is especially difficult to detect. Groups 
of cells are often found at portal spaces ; these are large 
and small mononuclears and granular cells, probably of 
the hematopoietic system. It is possible that blood 
formation is performed in the liver and spleen in some 
adult birds but such a function is denied for the 
mammal except under ver}^ unusual conditions of bone 
marrow atrophy. 
