In the carpus of the Mammalia there are usually two additional bones developed in the tendons of the flexor muscles, one on each side of the carpus, which may be called the radial and ulnar sesamoid bones; the latter, which is the more constant and generally larger, is commonly known as the pisiform bone. The fourth and fifth carpals of the distal row are always united into a single bone, and the centrale is very often absent. As a general rule all the other bones are present and distinct, though it not unfrequently happens that two may have coalesced to form a single bone, or one or more may be altogether suppressed. The following table shows the principal names in use for the various carpal bones,—those in the second column being the terms generally employed by English anatomists:— _Radiale_ = Scaphoid = _Naviculare_. _Intermedium_ = Lunar = _Semilunare_, _Lunatum_. _Ulnare_ = Cuneiform = _Triquetrum_, _Pyramidale_. _Centrale_ = Central = _Intermedium_ (Cuvier). _Carpale_ 1 = Trapezium = _Multangulum majus_. _Carpale_ 2 = Trapezoid = _Multangulum minus_. _Carpale_ 3 = Magnum = _Capitatum_. _Carpale_ 4 } = Uneiform = _Hamatum_, _Uncinatum_. _Carpale_ 5 } The radial and ulnar sesamoids are regarded by Bardeleben[12] as the rudiments of a prepollex and a postminimus digit; the primitive number of digits being thus supposed to have been seven. These bones have been observed in all orders of mammals having five complete digits. Occasionally, as in _Pedetes caffer_, the so-called prepollex consists of two bones, of which the distal one bears a distinct nail-like horny covering. In _Bathyergus maritimus_ the pisiform, or postminimus, is likewise double; the two elements being regarded by their describer as representing the carpal and metacarpal of the presumed seventh digit. Similarly in the posterior limb the tibial sesamoid, and a fibular ossification corresponding to the pisiform, are regarded as representing a prehallux and a postminimus.