Insertion. - Into the upper third of the ridge on the outer part of the humerus.
Action. - This is a muscle of considerable power and importance, being specially instrumental in raising the limb from the ground and carrying it forward in progression. Upon it chiefly depends that grand shoulder action so much admired in our best harness horses.
It is capable of acting in two directions: when the head is fixed it raises and advances the fore-limb; when the fore-limb is fixed, as in a standing posture, it draws the head to one side, or, acting with its fellow on the opposite side, it pulls it downward.