Every single metacarpal includes a foundation, shaft in addition to a head. The medial and lateral surfaces in the metacarpals are concave, making it possible for attachment in the interossei muscles. Moreover, the deep head in the flexor pollicis brevis is innervated with the deep branch on the ulnar nerve. https://www.theorthopaedicandpainpractice.com/what-are-the-different-bones-found-in-my-hand/