masses joined by an intervening narrower 
portion. 
Tlie placenta of the bisulca is divided 
into numerous cotyledons, the structure of 
which is very interesting as it elucidates 
the whole physiology of this organ. The 
parts designated by this appellation are cer- 
tain fleshy excrescences (glandulae uterinaa) 
produced from the surface of the impreg- 
nated uterus, and having a corresponding 
number of flocculent fasciculi of blood-ves- 
sels (carunculaj) which grow from the ex- 
ternal surface of the chorion implanted in 
them. Thus the uterine and fetal portiotis 
of tlie placenta are manifestly distinct from 
each other, and are easily separable as the 
foetus advances to maturity. 'I'he latter 
only are discharged with the after birth, 
while the former, or the cotyledons, gra- 
dually disappear from the surface of the 
uterus after it has parted with its contents. 
The number and form of these excrescences 
vary in the different genera and species. 
In the sheep and cow they sometimes 
amount to a hundred. In the former ani- 
mal and the goat they are, as the name im- 
plies, concave eminences ; while on the 
contrary, in the cow, deer, &c. their surface 
is rounded or convex. 
The trunks of the veins which pass from 
the placenta or carunculae, and of the ar- 
teries whicit proceed towards these parts, 
are united in the umbilical chord, which is 
longer in the human embryo than in any 
other animal. 
In the foal, as in the child, the chord pos- 
sesses a single umbilical vein ; whilst most 
other quadrupeds have two, which unite, 
however, into a common trunk near the 
body of the foetus, or just within it. 
The amnion, or innermost of the two 
membranes of the ovum, which belongs to 
the pregnant woman, as well as to the mam- 
malia, is distinguished in some of the latter, 
as for instance in the cow, by its numerous 
blood-vessels ; while on the contrary, in the 
human subject it possesses no discernable 
vascular ramification. 
Between the cliorion and amnion thei'e 
is a part found in most pregnant quadrupeds, 
and even in the cetacea, which does not be- 
long to the human ovum, viz. the allantois 
or urinary membrane. The latter name is 
derived from the connection w'hich this 
part has, by means of the urachus, with the 
urinary bladder of the fetus ; whence the 
watery fluid which it contains has been 
regarded as the urine of the animal. The 
term allantois has arisen from the sausage- 
E ANATOMY. 
like form which the part possesses in the 
bisulca and the pig ; although this shape is 
not found in several other genera and spe- 
cies; thus in the hare, rabbit, guinea-pig, 
&c. it resembles a small flask ; and it is oval 
in the pole-cat. It covers the whole inter- 
nal surface of the chorion in the solidungula, 
and therefore incloses the foal with its am, 
nion. It contains, most frequently in these 
animals (although not rarely in the cow), 
larger or smaller masses of an apparently 
coagulated sediment in various forms and 
number, which has been long known by the 
singular name of the horse-venom, or hippo- 
manes. 
Some orders and genera of mammalia 
resemble the human subject in having no 
allantois, as the quadrumana and the hedge- 
hog ; nay, in the latter animal, the urinary 
bladder has no trace whatever of urachus. 
ON THE INCUBATED EGG. 
The various vital processes of nutrition 
and formation which are carried on in the 
fetus of the mammalia while in its mother's 
body, and by means of the most intimate 
connexion with the parent, are effected in 
the incubated chick by its own powers, 
quite independently of the mother, and 
without any extraneous assistance, except 
that of the atmospheric air and a certain 
degree of warmth. 
The egg is covered, within the shell, by a 
white and firm membrane (membrana albu- 
minis) which contains no blood-vessels. 
The two layers of tliis membrane, which in 
other parts adhere closely to each other, 
leave at the large end a space which is filled 
with atmospheric air. 
T.his membrane includes the two white.?' 
of the egg, each of which is surrounded by 
a delicate membrane. The external of 
these is the most fluid and transparent ; 
the inner one thicker and more opaque ; 
they may be separated in eggs which are 
boiled hard. 
The inteinal white sunounds the yolk, 
which is contained in a peculiar membrane 
called the yolk-bag. From each end of this 
proceeds a white knotty body which ter- 
minates in a flocculent extremity in the 
albumen. These are called the chalazae, or 
grandines. 
A small round milk-white spot, called 
the tread of the cock (cicatricida, or ma- 
cula), is formed on the surface of the yolk- 
bag. It is surrounded by one or more 
whitish concentric circles (halones, or cir- 
culi), the use of which, as well as thqt of 
