Antagonististic Muscles Associated with the Humerus
The humerus is protracted by contraction of the supraspinatus muscle. The supraspinatus originates along the cranial, lateral surface of the scapula and inserts on the head of the humerus. When it contracts the forearm moves toward the head. The clavodeltoid (not shown here) originates on the clavicle and inserts on the deltoid ridge. It also helps to protract and abduct the humerus.
Retraction of the humerus is controlled by the contraction of the spinodeltoid and the teres major. The spinodeltoid originates along the spine of the scapula and inserts on the deltoid tuberosity of the humerus. The teres major originates from the caudodorsal surface of the scapula and inserts on the proximal third of the humerus. The action of these two muscles draws the humerus toward the tail, however the teres major tends to rotate the humerus toward the midventral line (adduct) while the spinodeltoid tends to rotate it in the opposite direction (abduct).
Click here to view the muscles associated with the shoulder. Find the three muscles that help retract the humerus (infraspinatus, teres major, spinodeltoid.) The infraspinatus is partially covered by the teres major and the spinodeltoid. Now test yourself to see how many other muscles you can identify.
Click to locate the clavodeltoid, one of the muscles that protracts the humerus. Then review the other muscles. The red arrow is pointing to a lymph gland.
The clavodeltoid and the spinodeltoid combine to Abduct the humerus. This type of motion moves the humerus away from the ventral midline. An antagonistic group of muscles the pectoralis major and the pectoralis minor have the opposite function. They adduct the humerus, moving it toward the midventral line.
Click to see the adductors of the humerus.
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