AND DEVELOPMENT OF THE LIVER. 
129 
of Mammalia of the relation obtaining- between the condition of the liver and the 
amount of respiration: the cells of a porpoise’s liver were granular nucleated 
bodies, containing rarely a single oil-drop ; nor was there more than a very minute 
quantity of oil in a free state throughout the gland, — a contrast most complete to the 
condition of the hepatic parenchyma in its co-inhabitants of the watery element, 
which respire not by lungs, but by branchiae. 
Development. 
The development of the liver is described by Muller, with whom Valentin and 
others agree, as being formed on the fourth day of the incubation of the chick by a 
conical protrusion of the intestine, which soon acquires walls of considerable thick- 
ness, in the substance of which the ducts proceed to ramify ; some of the “ biliferous 
canals” however being apparently formed independently in the blastema itself. A 
different account is given by Reichert, who states that the rudimentary mass of the 
liver, as well as that of the pancreas, is merely a cellular growth from the surface of 
what he calls “ membrana intermedia,” which appears to be a layer of cells deve- 
loped from the germinal disc, corresponding to the vascular and mucous layers, and 
destined to give origin to the vertebral, cutaneous, and sanguineous systems, and 
the digestive system, with the exception of its mucous membrane. 
The following observations fully confirm the opinion of Reichert, so far as regards 
the independent origin of the liver ; with respect however to some other points, the 
description which I venture to offer is in some degree different from any with which 
I am acquainted. On the morning of the fourth day I have found in the chick the 
chorda dorsalis and the rudiments of the vertebrae perfectly distinct ; below these was 
a longitudinal fold with its convexity downwards, which was probably one of the 
‘‘ visceral laminae towards the anterior part of this, and just behind the heart, there 
was a slight convex prominence, with a vascular free border, which appeared as a 
growth from the germinal membrane; this was probably the rudiment of the liver: 
no trace could be discerned of anything like an intestine. In another specimen about 
the same period, it was noticed that the developing vessels were very patchy and 
irregular, that in some parts there were merely spots or short streaks, and that 
though containing well-formed blood-globules, they did not appear to have distinct 
parietes. On the fifth morning the liver was quite distinct ; it appeared as a some- 
what reddish yellow mass situated just behind the heart, and presenting a free convex 
border below ; above it ran the oesophagus curving forward and upwards, behind it 
was the stomach and the recently developed intestine. The border of the liver was 
pretty distinct in the whole of its circumference ; a narrow space clearly intervened 
between it and the oesophagus and stomach, and there did not appear to be the 
slightest trace of the liver being derived from either of them ; it seemed manifestly a 
separate and independent formation. The intestine distinguished from the oesophagus 
and stomach appears to be developed in the following manner, which I think has not 
MDCCCXLIX. s 
