Flying Conductors

The abductor pollicis longus in flying squirrels is a prominent muscle, despite the fact that the thumb is minuscule. It takes origin from the extensor surfaces of the radius and ulna, as in other squirrels, and the tendon passes through the radial compartment of the wrist superficial to the tendons of the extensor carpi radialis brevis and longus muscles. The tendon of the abductor pollicis longus bifurcates with one part inserting on the metacarpal of the thumb and the other part inserting on the falciform bone, the tendon to the falciform bone is the larger of the two. Between the dorsal surface of the falciform bone and the palmar surface of scapholunate, there is an arthrodial joint. The falciform is connected to the styliform cartilage on the opposite side of the wrist by a
The styliform falciform ligament attaches to the styliform cartilage distal to its hinge. Because the falciform bone in flying squirrels is relatively mobile, this anatomical arrangement should allow the abductor of the thumb to pull the falciform bone toward the radial side of the hand, which in turn will pull on the styliform falciform ligament and extend the cartilage to support the curved wing tip. Researchers tested this in preserved specimens of Petaurista and in both preserved and fresh specimens of Glaucomys by pulling on the tendon of the abductor pollicis longus to simulate flexion of this muscle. With the hand abducted and dorsiflexed, a pull on the tendon of the abductor caused the wing tip to extend and to be held in a normal gliding position. The flexor carpi ulnaris muscle, innervated by the ulnar nerve, takes origin by two heads one from the medial side of the proximal end of the ulna and one from the medial epicondyle of the