A TENDON-LOCKING MECHANISM IN 2 CLIMBING RODENTS, MUSCARDINUS-AVELLANARIUS AND MICROMYS-MINUTUS (MAMMALIA, RODENTIA)

Having compared the microanatomy of the toes of a terrestrial to two c limbing species, adaptations were found in the flexor tendons and in t he integument. In contrast to Crocidura russula, both Muscardinus avel lanarius and Micromys minutus have a tendon-locking mechanism (TLM) th at is engaged when the middle phalanx is bent. A ventral thickening of the flexor tendon is situated deep to a thickened portion of the vent ral tendon sheath. When twigs or stalks are grasped, the TLM allows le ss muscular energy to be expended. In C. russula glands are restricted to the terminal pads, but in the climbing species they occur in the s ole of the toes as well. In the reed-living M. minutus knob-shaped int egumental thickenings, together with the digital pads, stabilize the g rip. In contrast the arboreal M. avellanarius often climbs thick branc hes and shows adaptations for pressing the sole of the feet against th e surface. Thereby the tendon attached to the plantar integument of th e toes transfers the muscle force directly to the bark. Unlike the oth er digits on the forefeet of both climbing species, no TLM is present in the anterior digit. In M. minutus this short digit is twisted towar ds the palm and, with the carpal pads, provides an abutment against th e grasping fingers. In M. avellanarius the anterior digit has very thi n tendons and is that much reduced in length that it is completely int egrated into the digital pad where it acts, at best, as a lateral supp ort of the pad. (C) 1996 Wiley-Liss, Inc.