📝 STANDARD DESCRIPTION:
Type: Intrinsic, Brachial (Biarticular)
Origin: Supraglenoid tubercle of scapula
Insertion: Radial tuberosity (proximal medial radius) and medial collateral ligament of elbow
Function: Flexes elbow; extends shoulder via reciprocal tension.
Stay Apparatus: Lacertus fibrosus connects to Extensor Carpi Radialis (passive carpal extension).
📚 DETAILED DESCRIPTION:
THE STAY APPARATUS ANCHOR
Despite its name, the bovine biceps brachii has only one head (unlike the two-headed human version). It is a powerful biarticular muscle crossing both shoulder and elbow joints.
SUPRAGLENOID ORIGIN: Originates from the supraglenoid tubercle (cranial margin of glenoid cavity), placing it cranial to the shoulder joint axis.
PASSIVE STAY MECHANISM: The muscle sends a fibrous band called the lacertus fibrosus to the tendon of the Extensor Carpi Radialis. While less developed than in the horse, this structure contributes to the passive stay apparatus by preventing flexion of the carpus while standing without muscular effort.
BIO-TENDINOUS COMPLEX: The tendon bridges the cranial aspect of the shoulder and passes through the intertubercular (bicipital) groove (bicipital groove), where it is protected by the transverse humeral retinaculum.
DUAL JOINT ACTION: Flexes the elbow joint (primary action) and extends the shoulder joint via its cranial position relative to shoulder center of rotation. The biceps brachii 'tension band' principle helps stabilize the shoulder during weight bearing.
// COMPARATIVE ANALYSIS
| HORSE |
Lacertus fibrosus is massive and primary stay apparatus component; biceps tendon is larger. |
| DOG |
True two heads; no significant stay apparatus contribution. |
CLINICAL RELEVANCE
Bicipital Bursitis: Inflammation of bicipital bursa in the intertubercular groove causes lameness. Radial Nerve Association: Proximal radial nerve injury affects elbow extension, but biceps flexion is unopposed, creating imbalance.
