Developmental anatomy of the palmar aponeurosis and its relationship to the palmaris longus tendon.

The palmar aponeurosis and the palmaris longus tendon were examined in 33 hands of gestational age from 5 weeks to term. At 5 weeks both the longitudinal and transverse layers of the palmar aponeurosis and the palmaris longus tendon were present and in continuity. The palmaris longus tendon was absent in five specimens and in these the longitudinal fibers of the palmar aponeurosis blended into the antebrachial fascia. Otherwise the structure of the palmar aponeurosis was similar in the presence or absence of the palmaris longus tendon. The staining characteristics of the palmaris longus tendon were those of tendon whereas the palmar aponeurosis stained like fascia. These observations, as well as the fact that the palmar aponeurosis has never been reported to be absent, support the view of Kaplan that the palmar aponeurosis and the palmaris longus tendon are separate anatomic structures, which develop independently and are associated only by anatomic proximity.