NORIEGA, K.C.*; REGA, E.A.: Heretofore undocumented variation of an intrinsic hand muscle in a juvenile baboon

Standard anatomical references for primate anatomy focus almost exclusively on adult morphology and rarely document the range of variability within structures. Dissection of the hands of a juvenile baboon (Papio sp.) demonstrates an accessory head to the m. opponens digiti minimi that is undocumented in adult specimens. This arrangement is similar to the pattern in Homo sapiens, a species with clearly acknowledged opposability in the hand. The opposability of the thumb and fingers is frequently cited as a key adaptation of humans, and its anatomical correlates have been suggested as uniquely human characters. Difficulties with this formulation arise as juvenile non-human primates have been known to utilize pad to pad opposition of the first and second digits. In addition, opposition of the fifth digital ray may be equally important in several activities linked to human cultural adaptation. We seek to document variability in the fifth digit as well as the thumb as part of an ongoing study into pedomorphosis in the anatomy and ultimately the manipulatory abilities of the adult human hand. These new data demonstrate the importance of intra-specific variability and ontogenetic information in making species-level characterizations.