The =first carpal= bone (Os carpale primum, trapezium) is a small
inconstant bone, commonly about the size and shape of a pea, which is
situated in the lower part of the internal lateral ligament behind the
second carpal bone.
This bone appears to be absent on both sides in about half of the
cases; in a good many subjects it is present on one side only. In size
it varies from a minute nodule to a discoid mass 10 to 12 mm. in
length. In exceptional cases it articulates with both the second
carpal and the second (inner) metacarpal bone, in other cases with the
former only, but in the majority of specimens no articular facet is
present.