The articulation between the second metacarpal and the capitate is considered uniquely specialized in
hominids. On the second metacarpal, the facet for the capitate is directed proximally, almost perpendicular to the facet for the third metacarpal, while the corresponding facet on the capitate is oriented distally. This is to receive compressive forces generated by the pad-to-pad
opposition between the thumb and the index finger. In contrast, in
apes, including fossil apes such as
Dryopithecus and
Proconsul, these facets are oriented in a
sagittal plane. In
quadrupedal monkeys these facets are oriented slightly differently due to their locomotor behaviour. In
Oreopithecus, a
Miocene hominid that became extinct , the orientation of the facet on the second metacarpal is similar to human conditions — an indication that it had the capability of pad-to-pad precision grip.
Oreopithecus also lacks the waisted capitate associated with apes and climbing still present in
Australopithecus. == Ossification ==