94 
FIRST CLASS OF THE VERTED RATED ANIMALS. 
portion than those of the Kangaroo. As the soles of their feet are very small, the 
metatarsi elevated, with the tail very long and hairy at its extremity, we perceive a 
striking dilfercnce in their mode of progression from that of the Kangaroos. At 
each leap the Jerboas fall upon their small fore feet, but they raise themselves very 
quickly by means of a long and heavy tail, serving as a counterpoise, and prevent- 
ing the body from falling backwards, which accident happens whenever the tail has 
been lost. 
Among the Rodentia, and especially with the Hares, where this disproportion be- 
tween the hinder and fore feet is not excessive, the animals usually lun at a full gal- 
lop ; but they avoid descending the declivities of the mountains at this pace, as the 
forcible action of their hinder legs, aided by the inequality of the ground, would 
occasion them to perform a somerset. In ascending, they possess, on the contrary, a 
considerable advantage over an ordinary quadruped, for the gradual rising of the 
ground counteracts the in(?quality in the length of the legs, and brings their body 
more nearly into the horizontal position. 
In the Martens, the Pole Cats, and the Ferrets, which have their feet small, and 
placed very far apart, the advance is always effected by a full gallop, the back being 
curved into an arch, in order to bring the two extremities nearer to each other, and 
to prevent tho abdomen from trailing on the ground. 
Among the terrestrial Mammalia, a great many species arc obliged to seek their 
food among the branches of trees. The greater number of these have their thumbs 
opposable to the other fingers, either on the four feet, as in the Apes and Makis, or 
on the hinder feet alone, as in several l^Iarsupialia. This arrangement gives to 
these animals the power of seizing the branches w’ith facility, and of applying tho 
entire palm of tho hand to the inequalities of surfaces. Other Mammalia, being de- 
prived of moveable fingers, make use of their long nails as hooks, which fulfil the 
same purpose, although rather in an imperfect manner, such as wc find in the Sloths 
anil Ant-eaters. 
Finally, among the climbing species we find many which make use of their tail 
as a fifth limb, on account of the surprising flexibility which it possesses, as well .as 
its power of rolling itself round the branches, and even of picking up very small and 
slender bodies. This tail, termed prehensile (^Cuuda pTchensilis)^ belongs more 
especially to some American Apes, to the Opossums, the Phalangers of the islands 
in the Indian Archipelago, to the Brazilian Porcupine {Ilystrix i)rchen$ilis\ and a 
few others. 
All those Slammalia, which, like Alan and the Apes, have the anterior extremities 
supplied with hands, possess at the same time complete clavicles, and one hand alone 
is sufficient to seize the food and bring it to the mouth. It is different witli all the 
other animals destitute of thumbs, and whose fingers, being moveable all together, 
and in one direction, are armed with crooked nails. In these animals, such as the 
Squirrels and Rats, the assistance of both hands is necessary to hold an object. 
Hence, while feeding, they are in the habit of sitting down, which enables them to 
use both of the anterior extremities with freedom. Those Carnassiers which have 
rudimentary clavicles, and whose paws are well funiishcd with claws, are obliged to 
hold their prey between the two fore paws, and tear it with their teeth. The Cats 
alone are able to carry with one paw to their mouth a very small portion of food by 
means of their sharp claws. 
Some Mammalia dig in the earth with great faciuly, and among them the ex- 
tremities are specially adapted for this purpose. The nails of the fore feet among 
the digging IMammalia are commonly very strong and short, .so that these animals 
are rarely swift runners, excepting perhaps the Jerboas, which hollow out their dwell- 
ings in the loose s-mds of the steppes. The Mole, the Scalops, and the Chryso- 
chloris, are especially remarkable for the strength of their hands, where all the fin- 
gers are united together, and form a kind of shovel or spade, very well adapted for 
removing the earth. In these animals the abdomen trails upon thi? ground. 
In general, we find that all the anomalous points in the organization of these ani- 
mals adapted for digging, may be reduced to two particulars — to modifications in tho 
anterior extremities, and proportional differences in the organa of sense. The first 
traces of these anomalies may be found in such Mammalia as burrow in the earth to 
shelter themselves and their young ones ; but they are most clearly seen in those 
animals whirh scarcely ever come from beneath the surface of the ground, but arc 
continually In the habit of seeking a subterranean subsistence, whether vegetable or 
animal. 
The first and most striking examples may be observed among the insectivorous 
Carnassiers, such as the Alole, the Chrysochloris, and a few neighbouring genera. 
Among these animals, we find that the anterior limbs are pvoportionably much more 
developed than the hinder, wliicb are very slender. Tho thorax forming the point 
of insertion for the muscles of the shoulder, acquires a peculiar solidity by the speedy 
ossification of the cartilages of the ribs, the pieces of the sternum, and by the exist- 
ence of a kind of hreasLwoik or medial crest. The clavicle being very strong and 
solid, projects much in front. The shoulder-blade is very broad, with the acromion 
and coiacoid processes dislincily pronounced, and indic.ating tho presence of muscles 
of a proportional size. 1 he sihouldcr loses much of its usual length to acquire a 
breadth so considerable, as almost to make it, square. Tlio two bones of the fore 
arm, though loss strong, are yet tolerably so ; and, finally, the hand, which is shaped 
like a shovel, is very short and broad, terminated by five very thick and cutting 
nails, and is still further augmented by a sharp bone as a supernumerary, which oc-* 
cupios the cubital margin. It may be added to this description, that the entire 
limb, which bears, at its insertion, upon the hiteral parts of the neck, is turned 
beneath and behind in such a way', that the hand acts constantly in those direc- 
tions. 
There is another modification in these animals, which properly belongs to the or- 
gans of motion. The nose or muzzle is modified to be an instrument fit for excavat- 
ing or ilicging, at tlie same time that it serves as a finder through the delicacy of its 
olfactory organ ; hence result the ossification of the cartilage separating the nostrils, 
the great development of tho muscles of the nose, and, finally, the great force of 
the extensor muscles of the head. 
Ill respect to tho organs of sense, wc may readily expect that the hearing 'Aill bo 
developed to an extent proportionably greater than in the other Mammalia, by meam 
of a larger drum, a very short auditive canal, a very wide orifice, and no kind of 
concha. On the contrary, the sense of sight continually diminirhes, until it ends by 
scarcely existing except iu a rudimentary form, as is found in many of the Rodentia, 
and especially in the Zemni (Spulax typhlus). In those species where the anterior 
limbs are a little less adapted for burrowing, the eyes disappear almost wholly, and 
the organ of hearing appears, on the contrary, to develop itself in an inverse pro- 
portion to the former sense. 
In respect to the Alaramalia capable of flight, these are of two kinds. Some have 
simply the skin of the sides extended behind the fore feet and before the hinder, as 
we see iu the Flying Cats (^Gnlenpiihec.ns)i the Squirrels, and the Flying Squirrels 
{Pteromys). The effect of these expansions of the skin merely consists in prevent- 
ing the body, when darting from a very elevated situation, the top of .a tree for ex- 
ample, from falling too heavily, and hence their function confines itself to that of a 
parachute. Other Mammalia, on tho contrary, do really fly, that is to say, they can 
elevate themselves by means of the movements of their anterior extremities, which 
are prodigiously developed and furnished with long fingers, united together by ex- 
pansions of a very fine skin ; these are ihe Bats. 
The first tendency towards the anomalous organization for flight is seen in tliose 
Mammalia which are disposed to seek their fond in trees, and hence are constitute«l 
so as to climb with facility. In fact, there is no Alamraiferous animal, before sus- 
taining itself in the air, which is not obliged to elevate itself to a height more or less 
considerable. The latter movement may be effected by a mere digital comprwsion 
of the fore and hind feet, as wc see in the Apes; or by embracing tlic tree, as in the 
Bear ; or, finally, by means of hook<, such as we sec in the Cats, the Sloths, and 
even in the Squirrels. Tlio first traces of that disposition by which these animals 
arc enabled to leave their elevated position, and maintain thcnwelves wltolly in the 
air, is found in some Rodentia nearly allied to the Squirrels, being the Pteromys or 
Flying Squirrels, which have on their flanks a fold of skin, as already described, and 
likewise in the Phalauifista or Flying Opossums. A still more perfect state of this 
organization is found in some species of Carnassiers nearly allied to .the Apes, such 
as the Galcopithccus, In these animals, the fore extremity is considerably elongated. 
The fore arm has acquired that peculiar ginglymoidiil arrangement, which has been 
assigned to the Cetacea for a different purpose ; and, as may bo easily supposed, the 
principal moving, and especially the pectoral, muscles are very largely developed. 
On the other hand, the hinder limbs have diminished very sensibly, and also the taiU 
which is almost wanting, in order to throw the centre of gravity of the body witbin 
the axis of the fore extremities. Tho most perfect form of this anomaly is, how- 
ever, seen in the Bats. 
The aquatic Mammalia are of two kinds ; some frequent the margins of lakes» 
rivers, or streams, into which they plunge occasionally to seize their prey, or to fin4 
the aquatic plants on which they feed. Their extremities are either wholly webbed, 
as in the palmatcd feet of the Ornithorhynchus, in which the expansion of the skin i» 
that of the palm or solo of the foot, and not merely of the fingers, as we find in the 
Otters and Cabiai.s. These animals have webs upon all the four feet, being different 
from the Beavers and Cheironectes, whose hinder extremities alone are \vebbed» 
while tho skin extcmUug between them is entire. In the Desmans, the feet are only 
scmi-palmatcd, and in the Hydromys, they are palmated for two-thirds of their 
length. 
The Ondatra, whoso mode of life is so analogous to that of the Beaver, has it* 
hinder feet fitted for swimming ; but instead of having tlie feet united by a mem-' 
branc, each of them is bordered on the right and left by a row of elongated, stiff* 
and serrated hairs, whicli cross each other by the points w’ith those of the adjoining 
fingers, thus forming a surface capable of offering suiHcieiit resistance to th^-' 
water. 
Among the marine Alammalia, the Seals and Alorses deserve to bo noticed 
the first place, because they arc supplied with all tho four extremities, of which 
anterior ha\e the fingers united, and armed with claws. Iu some species of Seals* 
being the Otarics of Peron, the skin on the tip of each finger is prolonged int® ^ 
long .anti narrow strap, forming a band. The hlxader feet, placed entirely at the ex- 
tremity of the body, also have apparent fingers, but these are united together by 
skin. Others, such as tho Lamantins and Dugongs, arc destitute of the hinder ex- 
tremities ; but all tho fingers of their limbs are invested by a thick skin, on which 
vestiges of nails arc to be found. Fitially, the proper Cetacea, which also have lh<* 
hinder extremities wanting, depart still more widely from tho quadrupeds, 
here fail to discover the slightest trace of nails. 'I’hese differences in the organize* 
tion of the extremities occasion corresponding variations in their mode of life. 
Seals arc very agile when in tho W'ater, and execute a number of evolutions 
movements in consequence also of the extreme flexibility of their vertebral column » 
but they walk with much apparent difficulty on the land. The Lamantins, 
gongs, and Scelleres {UytUia), have still greater difficulty iu leaving the water, an* 
remain like inert masses whenever they cliance to run aground upon a hank. The propc*" 
Cetacea do not voluntarily leave the sea, where they swim with a prodigious velo- 
city, by means of the movements of their tail and fins. In consequence of 
former being flattened from above downwards, and not compressed from right to loft* 
this organ moves chiefly in the vertical direction, instead of horizontally, as wc ^ 
iu the greater part of the Fushes. 
On comparing all aquatic Mammali.a with each other, and with the remaining 
mals of their class, we find that the organic modifications which have been experience 
by those Alammalia destined to reside more or less in the water, consist essentia T 
in the following particulars: — The Hairs which, in the ampliiblous animals, are o 
served to be short and exceedingly numerous, terminate in the Cot.acca by formii's 
an agglutinated or univeri^al envelope, as wc see in the Lamantins and Whales. ^ j** 
external Ear diminishes in size, until it ends, in certain Cetacea, by disappearing^ 
most wholly, so that it is scarcely possible to discover any vostigo of the cone 
The crystalline lens of the Eye is observed gradually to become more convex, and t 
approach insensibly towards the spherical form, which it acquires most completely 
species receding constantly in the water. ^Ve may further, remark tho absence 
