Figure 1. Bones of the left hand of the southern flying squirrel G. volans, showing tendons and ligaments invlolved in moving the styliform cartilage. (F =falciform bone; P =pisiform bone; S =scapholunate bone)
(adapted from: Thorington et.al. 1998)
Figure 2. Bones of the left hand of the eastern gray squirrel S. carolinensis.
|Forelimb function of G.volans:
--The connection of the styliform cartilage to both the pisiform bone and the base of the fifth metacarpal forms a hinge allowing the cartilage to be at a nearly right angle to the wrist.
--The falciform bone's mobility allows the abductor of the thumb to pull on the falciform bone, which in turn pulls on the styliform-falciform ligament and extends the styliform cartilage to support a curved wing tip.
--Moving the styliform cartilage causes tension and relaxation of the palmaris longus tendon. Both muscles may be invloved in retraction of the styliform cartilage and the wing tip. The involvement of the flexor carpi ulnaris may vary among species.
|Forelimb function of S. carolinensis
and S. niger:
--The flexor carpi ulnaris, present in S. carolinensis and S. niger though not depicted, acts as major flexor of the wrist. Similarly, the abductor palmaris longus is involved in hand closure.
--The transcarpal ligament, which is attached to the falciform bone, aids in thumb abduction and aduction. (Thorington et. al. 1998)
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