SOURCES OF MOTION AND SENSATION. 
43 
ANATOMY AND PHYSIOLOGY. 
Sir Charles Bell, in his paper on the brain 
begins by enumerating some of the impedi- 
ments which have retarded the discovery of 
tbe structure and functions of that organ. 1. 
The nature of the inquiry, since opposite re- 
sults must be expected in making investiga- 
tion upon a subject so delicate, In practice, 
we find effects produced by causes which 
seem quite inadequate. The presence of a 
small specula of bone will sometimes be 
attended by no consequence, and at other 
times will give rise to violent convulsions. 2. 
The disturbance of its circulation, for no 
organ depends more intimately upon the 
condition of the circulation within it than 
the brain. 3. The most frequent source of 
error is the obscurity which hangs over the 
subject, for not one of the grand divisions of 
the brain has yet been distinguished by its 
function. Hence have arisen imaginary 
theories which always tend to bury a science 
in obscurity. The present inquiries of the 
author are directed to the prosecution of the 
fact discovered by himself, that the nerves of 
motion and sensation originate from different 
sources. He follows up these tracts ; marks 
the portion of the brain to which they ulti- 
mately tend ; ascertains the effect of diseases 
on these parts, and compares the system with 
the anatomical details. The consequences 
which he has drawn from this investigation 
are : 1st, that sensibility and motion belong 
to the cerebrum : 2d, that two columns 
descend from each hemisphere, one of which 
the anterior, gives origin to the anterior 
spiral roots of the spinal nerves, and is dedica- 
ted to voluntary motion ; the other sends out 
the posterior roots of the spinal nerves, and 
the sensitive root of the fifth nerve, and is the 
column for sensation : 3d, that the columns 
of motion which come from different sides of 
the cerebrum, join and decussate in the me- 
dulla oblongata, and that the columns of 
sensation also join and decussate in the me- 
dulla oblongata : 4th, that these anterior and 
posterior columns bear,in every circumstance, 
a very close resemblance to one another, 
agreeing in their sensorial expansions, being 
widely extended in their hemispheres, and in 
every respect, except in the nervous fila- 
ments to which they give origin. 
The anatomical descriptions are illustra- 
ted by drawings, which will be found parti- 
cularly serviceable in unravelling, as far as 
anatomy can at present carry us, some of the 
intricacies of the cerebral organ. The pons 
varolii, we observe, in an especial manner, 
has received much attention from the distin- 
guished author. 
ON THE GENERATION OF THE 
MARSUPIAL ANIMALS. 
By R. Owen, Esq. 
The generation of Marsupial animals, which 
constitute a distinct tribe of mammalia, of 
which the kangaroo and opossum are the 
principal members, has hitherto been invol- 
ved in much obscurity. But Mr. Owen, who 
has been fortunate enough to have it in his 
power to examine the gravid uterus of a kan. 
garoo, has observed some important facts; 
The genera of this tribe are characterized by 
possessing a double uterus, and the true vagi- 
na is separated either wholly, or for a consi- 
derable extent, into lateral canals, while the 
digestive and generative tubes both terminate 
within a common cloacal outlet. In these 
respects, therefore, they approach the ovi- 
parous verterbrata. The foetus examined by 
the author was contained in the left uterus. 
No placental structure could be observed. 
The chorion was very thin. A transparent 
amnios enveloped this foetus. 3'he umbilical 
chord was two inches in length ; the uterus 
two inches in length, and above an inch in 
diameter. No perceptible trace of an allan- 
tois or urinary bladder could be detected ; 
but in another foetus two weeks old, a ura- 
chus was defected. The author concludes 
from the observations of others, coupled with 
his own, that the ovulum quits the ovisac as 
in ordinary mammalia. In the kangaroo 
uterine gestation continues 39 days ; in the 
opossum 26 days. The former has been de- 
termined with certainty in the Zoological 
Gardens, and therefore, overturns the state- 
ment of Hilaire, who made the period 4 
months. 
With regard to the relation between the 
size of the umbilical vesicle, the least vascu- 
lar placenta and a corresponding simplicity 
of brain, it appears that in the kangaroo, al- 
though shortly after birth the brain resembles 
in structure that of the lowest vertebrata, yet 
it afterwards assumes a more complex form 
than that of the opossums or dasyures. The 
individuals of the marsupial tribe seem low 
in intelligence, never manifesting any sign of 
recognition of their keepers or feeders, and 
being unable to utter vocalized sounds. When 
they are irritated they emit a wheezing or snar- 
ling guttural sound, the necessary apparatus 
for producing vocalized sounds being absent. 
In this respect they resemble the repiilia. 
In the author’s communication on the 
ornithorhyncus paradoxus, this idea of simila- 
rity and that lactation might co-exist wiilt a 
mode of generation essentially similar to that 
of the viper and salamander is fully confirm- 
ed. The regular gradation is traced which 
exists in different orders of mammalia, in 
which true viviparous or placental generation 
takes place, towards the ovo-viviparous or 
oviparous modes, in which the exterior co- 
vering of the ovum never becomes vascular. 
The ornithorhyncus is shewn to constitute a 
connecting link in the chain. Both of these 
papers are accompanied by plates. 
ON THE STRUCTURE AND FUNC- 
TIONS OF TUBULUR AND CELLU- 
LAR POLYPI AND OF ASCIDI^. 
By J. Lister, Esquire. 
Mr. Lister has observed the existence of 
currents within some zoophytes.* In the 
* The use of this term has been much rebro- 
bated by Lamark, but notwithstanding- his cen- 
sure it still continues to be employed by many 
distinguished naturalists ; and it is sufficiently 
expressive of a class of beings whose nature is 
Still involved in great obscurity. — E dit. 
