These bones, eight in number, are arranged in two transverse rows, of which one, the first, is superior or antibrachial; the other, the second, is inferior or metacarpal. Each of these rows contains four bones. Considered in the order we have indicated above--that is to say, proceeding from the radial to the ulnar side--they are thus named: scaphoid, semilunar, cuneiform, and pisiform, in the first row; trapezium, trapezoid, os magnum, and unciform, in the second. The number of these bones is not the same in all animals on account of the coalescence or absence of some. In each row the bones are placed side by side, with the exception of the pisiform, which being placed on the palmar surface of the cuneiform, produces a small projection in man, but a very pronounced one in quadrupeds. The pisiform is called the _hooked bone_ in some veterinary anatomies. If we consider the hook which it forms, we may recognise that the name is appropriate; but from the point of view of comparison with the human carpus, the name is unfortunate, for it creates confusion between the true pisiform (the fourth bone in the upper row), and the last bone in the lower row, which is the veritable unciform bone. We do not here seek for similarity of form, but homology of regions; and it is only by using the same names to denote the same things that we can succeed in determining such homology. Taken as a whole, the bones of the carpus form a mass which, by its superior border, articulates with the bones of the forearm, and by its inferior border is in relation with the metacarpal region. Its dorsal surface (anterior in quadrupeds) is slightly convex; its palmar surface (posterior in quadrupeds) is excavated, and forms a groove in which pass the tendons of the flexors of the fingers. This last, in man, has the appearance of a gutter, because of the prominences caused by the projection of the internal and external bones beyond their fellows. In quadrupeds the palmar groove is especially determined by the pisiform bone, of which we have just mentioned the great development. The region occupied by the carpus, in the unguligrades, is known as the _knee_; it would have been more appropriately named had it been called the _wrist_. The number of the metacarpal bones in mammals never exceeds five, but it often falls below it; the same is true for the digits. The first are generally equal in number to the latter; an exception is met with in ruminants, whose two metacarpals coalescing soon after birth, form but one bone; this, the _canon_ bone, articulates with two digits. The number of metacarpals and digits diminishes in proportion as the limbs cease to be organs of prehension, and become more exclusively organs of support and locomotion. The number of phalanges is two for the thumb and three for each of the other digits; except in the cetaceans, in which they are more numerous.