| Abstract: | This survey includes 58 genera of rodents from 26 families. The medial tarsal bone is probably unique to the order. Its presence, nature, and constant relationship with M. tibialis posterior are discussed. This muscle inverts and supinates the pes at the astragulo-navicular joint and moves the ankle. The M. flexor tibialis inserts on the medial sesamoid, on this sesamoid and the integument, on the sesamoid and the tendon of M. flexor fibularis, on the latter tendon only, or on the integument only. The occurrence, nature, and cam-like action of the sesamoid are described. A distal segment of the tendon of M. flexor tibialis usually extends from the sesamoid to either the first phalanx of the first digit or to fascia of an adjacent muscle. Functions of the medial sesamoid include (1) stabilization of the tendon of M. flexor tibialis, (2) deflection of this tendon to benefit flexion of the first phalanx, (3) winching of the medial tarsal ligament to flex the first metatarsal, (4) control of the angle of insertion of the tendon to provide flexion or abduction of the first digit as appropriate during swimming, (5) mechanical multiplication of the tension in the tendon between the segments proximal and distal to the sesamoid, and (6) longitudinal folding of the sole of the pes to grip the substrate, as in climbing. |
