The radius forms the chief bone of the fore-arm in the mammalia, generally speaking ; the ulna is a small slender bone, terminating short of the wrist in a point, and often consolidated with the ra dius, as in -the horse and ruminating ani mals. A few genera, which have great and free use of their anterior extremity, have the power of pronation and supina tion. But this power diminishes, as the fore-feet are used more for the purpose of supporting the body in standing, and in progression. In this case, indeed, the ex tremity may be said to be constantly in the prone position, as the back of the carpus and toes is turned forwards.
The lower end of the ulna is larger than that of the radius in the elephant ; but this circumstance occurs in no other in stance.
The radius and ulna exist in the seal, manati, and Whales, but in a flattened form.
Several genera of mammalia possess a hand ; hut it is much less complete, and consequently less useful than that of the human subject, which well deserves the name bestowed on it by Aristotle, of the organ of all organs. The great superiori ty of that most perfect instrument, the hu man hand, arts.:s from the size and strength of the thumb, which can be brought into a state of opposition to the fingers, and is hence of the greatest use in grasping spherical bodies, in taking up any object in the hand, in giving us a firm hold on whatever we seize ; in short, in a' thousand offices, which occur every moment of our lives, and which either could not be accomplished at all, if the thumb were absent, or would require the concurrence of both hands, instead of be ing done by one only. Hence it has been justly described by Albinos as a second hand, " manus parva majori adjutrix," de sceleto, p. 465.
All the simim possess hands ; but, even in those which many be most justly stiled anthropomorphous, the thumb is small, short, and weak ; and the other fingers elongated and slender. In others, as some of the cercopitheci, there is no thumb, or at least it is concealed under the integuments ; but these animals have kind of fore-paw, which is of some use in seizing and carrying their food to the mouth, in climbing, &c. like that of the squirrel. 'Ore genus lemur has also a separate thumb. Other animals, which have fingers sufficiently long and movea ble for seizing and grasping objects, are obliged, by the want of a separate thumb, to hold them' by means of the two fore paws ; as the squirrel, rat, opossum, &c. Those which are, moreover, obliged to rest their body on the fore-feet, as the dog and cat, can only hold objects by fixing them between the paw and the ground. Lastly, such as have the fin
gers united by the integuments, or en closed in hoofs, lose all power of prehen sion.
The metacarpus is elongated in those animals, where the toe only touches the ground in standing or walking ; and con stitutes the part which is commonly call ed the fore-leg ; as the carpus is termed the knee.
The number of metacarpal bones is the same with that of the fingers or fore-toes, except in the ruminating animals. Even in these there are two distinct metacar pal bones, lying close together before birth : the opposed surfaces first become thinner, then are perforated by several openings, and at last disappear ; so that the adult animal has a single cannon bone, possessing a common medullary cavity, internally, and marked on the out side with a slight groove at the place of the original separation. There is there fore but one metacarpal bone in the adult for the two Wes. The structure of the metatarsus is the same.
The single finger or fore-toe of the horse is composed of the usual three phalanges ; the first, which is articulat ed to the cannon, is called the pas tern : the 2c1 is the coronet ; and the 3d the os basis, or coffin bone, on which the hoof rests. There are also two sesamoid bones at the back of the pastern joint ; and an additional part, 'called the shuttle-bone, connected to the coffin.
In those animals which have five toes, as the carnivora, &c. that which lies on the radial side of the extremity, and is therefore analogous to the thumb, is parallel with the others ; and the animal, consequently, has not the power .of grasping any object. The last phalanx in these supports the nail of the animal ; and sends a process into its cavity. These parts are so connected, that nail is naturally turned upwards, and not towards the ground : so that its point is not injured in the motions of the animal. The phalanx must be bent, in order to point the nail forwards or down. wards.
The order of rodentia have generally five toes ; that which corresponds to the thumb being the shortest.
The elephant has five complete toes ; but they are almost concealed by the thick skin.
The pig has four toes ; two larger ones, which touch the ground ; and two smaller behind these, which do not reach so far. There is also a bone, which seems to be the rudiment of a thumb.
The phalanges of the cetacea are flat tened, not moveable, and joined together in the fin.