The frequency of the Musclus palmaris longus was studied by observing its tendon in vivo in 379 Amazon Indians belonging to the following tribes: Tucano, Tariana, Tiriyo, Desana, Piratapuya, Macu and Arapaso. The muscle was not observed in 14 individuals (3.7% ± 1.0) either unilaterally or bilaterally and in 24 of 758 limbs (3.1% ± 0.6). No statistically significant difference was observed in the frequency of the muscle among the different tribes. Bilateral absence was significantly more frequent than the unilateral one; absence in females was more frequent than in males.

The frequency of palmaris longus agenesis in Amazon Indians agrees with reported values for Negroids and Mongoloids and is considerably lower than that generally reported for the Caucasoids.