306 
Wagner, (Hecker’s Literarische Annalen, Fe- 
bruarheft, 1834,) but also in works in our own 
language, as in Hodgkin’s Translation of Ed- 
wards’s Influence of Physical Agents on Life, 
Appendix, p. 438, 1832, have rendered the fact 
sufficiently familiar. But the connection of 
this well-known appearance with the mode of 
formation or multiplication of the blood par- 
ticles had not before attracted the attention it 
seemed to deserve; on this subject I have else- 
where remarked : “ In some of the granulated 
blood-discs of the Perameles the subdivisions 
potdecing that appearance were fewer and 
arger, and were separated by deeper clefts 
than I had before observed ; they suggested to 
me the idea that the blood-disc was under- 
going a spontaneous subdivision into smaller 
vesicles, and, although my observations are not 
at present sufficiently numerous to warrant the 
pi tegen that the development of smaller ve- 
sicles within itself is a normal property of the 
ordinary coloured vesicle or blood-disc, yet the 
obscurity which still hangs over the origin and 
reproduction of the blood-discs, and the unex- 
pected constancy of the granulated form in a 
greater or less proportion of them while recent, 
and floating in the serum, in different species of 
animals examined by me, makes me unwilling 
to suppress any idea naturally arising out of 
such observations and likely to be suggestive 
of examination of the same appearances by 
other microscopical observers.”* The general 
form of the blood-vesicles of the Perameles is 
the usual circular flattened disc: they presented 
a greater variety of size than in the Daysurus, 
but upon the whole a larger average diameter, 
Viz. y,4;th of an English inch. 
Phalangista Vulpina.—Average diameter of 
blood-dise 5th inch, 
Petaurus sciureus.—Ditto ditto yyth inch. 
Macropus penicillatus—Do. do. z45th inch. 
Macropus major.—Ditto ditto 45th inch. 
Phascolomys Vombatus.—Do. do. ,t;3th inch. 
The results of the present observations on 
the blood of the Marsupial quadrupeds cor- 
respond generally with those obtained from the 
placental Mammalia, inasmuch as the blood- 
discs of the species which derives its nutriment 
from the greatest variety of organized substances, 
as the Perameles, which subsists on insects, 
worms, and the farinaceous and succulent ve- 
getables, are Jarger than those of the strictly 
carnivorous Dasyure, and of the herbivorous 
Kangaroo, the blood-discs of the latter, like 
those of the placental Ruminant, being the 
smallest, though not in the same proportion. 
In each natural group of Marsupialia there is 
a direct relation between the size of the blood- 
disc and that of the species, 
Heart.—The heart is inclosed in a pericar- 
dium, and situated in the same relation to the 
lungs, mediastinum, and thoracic cavity as in 
the Rodent and most other mammiferous quad- 
* Medical Gazette, 1839, l.c. My hypothesis 
has received a certain degree of confirmation by 
the subsequently published observations on the 
division of the corpuscles of the blood by Mr. 
Quekett, (Med. Gazette, January, 1840,) and by 
Dr, Martin Barry, Philos. Trans. 1840, p- 595. 
MARSUPIALIA. 
rupeds. It offers no peculiarity in its general 
oe form. The apex is less obtuse i 
some species, as the Phalanger and Wombat, 
than in others, as the Kangaroo. The serous 
layer of the pericardium is reflected upon thi 
large vessels near to the heart. The fibrouw 
layer of the pericardium adheres to the sternut 
in the Kangaroo. The appendix of the rig 
auricle is always divided into two r 
cesses, (a, a, figs. 131 and 132,) one in fre 
and the other behind the trunk of the a 
Fig. 131. 
¢ 
a 
Heart of the Kangaroo. 
Besides this characteristic modification of | 
external form, the right auricle presents som 
still more essentially marsupial conditio 
in its interior. There is no trace, for 
of a ‘ fossa ovalis’ or an ‘ annulus ovalis 
any marsupial animal;* and the absence 
these structures, which are present in the 
of all the placental Mammalia, doubtless” 
lates to the very brief period during which | 
auricles intercommunicate in the Marsupis 
and to the minute size, and in other resp 
incompletely developed state, at which 1 
young marsupial animal respires air by 
lungs, and has the mature condition of | 
pulmonary circulation established. The 
and left auricles intercommunicate by 
oblique fissure in the uterine embryo of 
Kangaroo, when two-thirds of the period | 
gestation is past, but every trace of this fost 
structure is obliterated in the subsequent gro 
of the heart; so that in the mature animal 
wide terminal orifice of the posterior cava 1 
* Physiological Catalogue, Mus. Royal Ce lege 
of Surgeons, 4to. vol. ii. p. 52. a 
