Overview
Its belly lies caudolateral to the extensor carpi radialis. Its tendon crosses the dorsal surface of the carpus and splits into four, one for each weight-bearing digit.
Claw retraction at rest does not depend on this muscle: elastic dorsal ligaments, running from the middle to the distal phalanx, keep the claw sheathed. The claw is protruded when the deep digital flexor contracts.
Origin
Lateral epicondyle of the humerus.
Insertion
Middle and distal phalanges of digits II to V, on their dorsal surface.
Action
Extends the digital joints and the carpus.
Innervation
Radial nerve (n. radialis).
Clinical relevance
- With a radial nerve injury the cat cannot extend its digits and knuckles over onto the dorsum of the paw.
- Onychectomy (declawing) amputates the distal phalanx and with it the insertion of this tendon. It is banned in many countries and opposed by veterinary organisations.