This is a long, broad, fleshy muscle, extending from the top of the head downward along the side of the neck over the point of the shoulder to the humerus or upper arm bone.

Origin. - Above from the mastoid process and crest of the occipital bone, and from the transverse processes of the first four cervical vertebrae.

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.