Sesamoids of the pollical metacarpophalangeal joint and the evolution of hominoid hands

Sesamoids of the metacarpophalangeal joint are tiny bones located in the volar plate and articulated with the metacarpal head. Almost all living humans have radial and ulnar sesamoids in their pollical metacarpophalangeal joints. These bones protect and guide the tendon of the long (= extrinsic) pollical flexor. Whereas this condition is considered to be primitive for primates, living great apes have a tendency to lose these pollical sesamoids....