Overview
It is the most cranial and bulkiest muscle of the equine forearm. Its belly narrows in the distal half of the forearm and its tendon crosses the dorsal surface of the carpus inside a synovial sheath. In the proximal forearm it receives the lacertus fibrosus of the biceps brachii.
Origin
Lateral supracondylar crest of the humerus and radial fossa.
Insertion
Tuberosity of the third metacarpal bone (tuberositas ossis metacarpalis III), on the dorsal surface of the proximal cannon bone.
Action
Extends the carpus and flexes the elbow.
Innervation
Radial nerve (n. radialis).
Clinical relevance
- Through the lacertus fibrosus it is part of the stay apparatus of the thoracic limb: the tension of the biceps, passed on to this tendon, helps keep the carpus extended without muscular effort.
- Wounds over the dorsal carpus can open its tendon sheath or the joint capsule; any wound in this area calls for ruling out contamination of synovial structures.