COMPARATIVE ANATOMY. 
18, the elephant 19, and the two-toed sloth 
23 pairs. The sternum is generally cylin- 
drical and jointed. 
BOXES OF THE UPPER EXTREMITY. 
We may assert, as a general observation, 
that the four component parts of the upper 
extremity, viz. the shoulder, arm, fore-arm, 
and hand, can be clearly shewn to exist in 
the anterior extremities of all mammalia ; 
however dissimilar they may appear to each 
other on a superficial inspection, and how- 
ever widely they may seem to deviate from 
the human structure. 
Whenever an animal of one class resem- 
bles those of a different order in the form 
and use of any part, we may be assured 
that this resemblance is only in externals 
and that it does not affect the number and 
arrangement of the bones. Thus the bat has 
a kind of wings ; but an attentive examina- 
tion will prove, that these are really hands, 
with the phalanges of the fingers elongated. 
The dolpliin, porpoise, and other cetacea, 
seem to possess fins, consisting of a single 
piece. But we find, under the integuments 
of the fin-like members, all the bones of 
an anterior extremity, flattened in their 
form, and hardly susceptible of any motion 
on each other. We can recognise very 
clearly the scapula, humerus, bones of the 
fore-arm, and a hand consisting of five 
fingers : the same parts, in short, which 
form the anterior extremity of other mam- 
malia. See Tyson’s “ Anatomy of a Por- 
poise,” fig. 10 and 11 : also Blasii “ Anato- 
mia Animalium,” tab. 51, fig. 3, 4. 
The fore-feet of the sea-otter, seal, wal- 
rus, and manati, form the connecting link 
between the anterior extremities of otlier 
mammalia, and the pectoral fins of the 
whale kind. The bones are so covered and 
connected by integuments, as to constitute 
a part, adapted for the purposes of swim- 
ming : but they are much more developed 
than in the latter animals, and have free 
motion on each other. 
The cold-blooded quadrupeds bear great 
analogy in the four component parts, and 
in the general structure of their anterior 
extreraitiesj to tlie warm-blooded ones. 
See Caldesi’s “ Observations on the Turtle,” 
tab. 3, fig. 1, 4, 5. 
The bones of the wing of birds have a 
considerable and unexpected resemblance 
to those of the fore-feet of the mammalia. 
And the fin-like anterior member of the 
penguin contains, within the integuments, 
the same bones as the wings of other birds. 
The clavicle supports the anterior extre- 
mity, and maintains the shoulder at its proper 
distance from the front of the trunk. It ex- 
ists, therefore, in all such animals as make 
much use of these members, whether for the 
purpose of climbing, digging, swimming, or 
flying. It has, indeed, been supposed to 
be confined to Linnaeus’s order Primates 
(in which he includes man, the quadruma- 
nous animals, and bats). It will be found 
in the squirrel and beaver, who use their 
front extremities for the purpose of holding 
objects, rather than for that of supporting 
the body : in the mole, who employs them 
for digging, &c. &c. Many other animals 
have in its place an analogous small bone, 
merely connected to the muscles, and called 
by Vicq d’Azyr, os claviculare, to distinguish 
it from the more perfect clavicle. This 
is the case with most of the ferae, and some 
glires. It does not exist, on the contraiy, 
in snch as use their fore-feet merely for the 
purpose of progression ; since these limbs 
must be brought more forwards on the chest 
that they may support that part, by being 
placed perpendicularly under it. In the 
genera, which hold an intermediate rank 
between these ; which do not enjoy such 
an extensive utility of the fore-feet as the 
first division of animals; and are not so 
limited in their employment as the second, 
the clavicular bones, or imperfect clavicles 
exist. 
In ruminating animals, and in the horse, 
the metacarpus consists of a single bone, 
called the cannon bone, which is very long 
when compared with that of man. The 
humerus becomes shorter, in proportion as 
the metacarpus is elongated : so that in ani- 
mals which have a cannon bone, the os hu- 
meri hardly extends beyond the trunk. 
Hence the mistakes which are made in com- 
mon language by calling the carpus of the 
horse his fore-knee, &c. 
The radius forms the chief bone of the 
fore-aim in the mammalia, generally speak- 
ing ; the ulna is a small slender bone, ter- 
minating short of the wrist in a point, and 
often consolidated with the radius, as in the 
horse and ruminating animals. A few ge- 
nera, which have great and free use of their 
anterior extremity, have the power of pro- 
nation and supination. But this power di- 
minishes, as the fore-feet are used more for 
the purpose of supporting the body in 
standing, and in progression. In this case, 
indeed, the extremity may be said to be 
constantly in the prone position, as the back 
of the carpus and toes is turned forwards. 
