BONES OF TOE 'UPPER tiTnEmrTy.
We may assert as a general observa tion, that the founcomponent parts of the upper extremities, 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 in spection, and however widely they may seem to deviate from the human struc ture.
Whenever an animal of one class re sembles those of a different order in the form and use of any part, we may be as sured that this resemblance is only in ex ternals, and that it does not affect the number and arrangement of the bones. Thus the bat has a kind of wings ; but an attentive examination will prove, that these are really hands, with the phalanges of the fingers elongated. The dolphin, porpoise, and other cetacea, seem to pos sess fins consisting of a single piece. But we find under the integuments of the fin like members, all the bones of an ante rior 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 mammalia. See Tyson's "Anato my of a Porpoise," fig. 10 and 11 : also Anatomia Anintalium," 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 other 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 swimming ; 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 ante rior extremities, to the warm-blooded ones. See Caldesi's " Observations on the Turtle," tab.3, fig. 1, 4, 5..
The hones of the wings of birds have a considerable and unexpeCted resemblance to those of the fore-feet of the mamma lia. And the fin-like anterior member of
the penguin contains, within the integu ments, the same bones as the wings of other birds.
The clavicle supports the anterior ex tremity, and maintains the shoulder at its proper distance from the front of the trunk. It exists, therefore, in all such animals as make much use of these mem bers, whether for the purpose of climb ing, digging, swimming, or flying. It has, indeed, been supposed to be confined to Linnatts's order Primates (in which he includes man, the quadrumanons ani mals, and hats.) 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 mus cles, and called, by Vicq d'Azyr, os clavi colare, to distinguish it from the more perfect clavicle. This is the case with most of the km, and some glires. It does not exist, on the contrary, in such 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 utilityt of the fore-feet as the first division of animals, and are not so limited in their employment as the se cond, the clavicular bones, or imperfect clavicles, exist.
In ruminating animals, and in the horse, the metacarpus consists of a sin gle bone, called the cannon bone, which is very long when compared with that of man. The humerus becomes shorter, it) proportion as the metacarpus is elongat ed; so that in animals which have a can non bone, the os humeri hardly extends beyond the trunk. Hence the mistakes which are made in common language, by calling the carpus of the horse his fore knee, &c.