Page:Equitation.djvu/102

 hand, permits four motions, extension, flexion, lateral inclination, and circumduction. Its movements are given by the muscles of the neck, obliquus capitis, sterno-maxillaris, rectus capitis, scalenus, longus coll, splenius, and angularis scapulae. All these muscles are either attached or related to the three other muscles which work the lower jaw. They are, therefore, most intimately concerned in the position which is given to the head and neck, through the sensation of the bits on the bars. It is the position of the head and neck which is the object of the flexions.

Two other especially powerful muscles of the neck are concerned primarily with locomotion. The rhomboideus is connected at the atlas region with the other muscles of the head and neck; but when this atlas region is fixed, it draws the shoulder forward and upward. It is, therefore, related to the scapulo-angularis and latissimus dorsi of the chest. The other large muscle, the mastoido-humeralis, has also one of its ends at the atlas region, and the other at the shoulder and chest. When the atlas region is fixed, at the same time that the rhomboideus lifts the fore leg, the mastoido-humeralis carries it forward. But if the chest region is the fixed point, this muscle draws the head and neck to one side. It is by means of the flexions that we obtain for these two muscles the fixed point in the atlas region. When the horse accepts contact of the bits on the bars, the rider controls directly the muscles of the head, and