The flexor retinaculum attaches to, and spans the distance between, the medial and lateral sides of the base to form the anterior wall of the so-called carpal tunnel. The sides and roof of the carpal tunnel are formed by the arch of the carpal bones.
Each of the five metacarpals is related to one digit:
Metacarpal I is related to the thumb.
Metacarpals II to V are related to the index, middle, ring, and little fingers, respectively (Fig. 7.94).