attached to humerus muscle of shoulder mastoid process of temporal bone brachiocephalic muscle The brachiocephalicus is more complex than other muscles of the forelimb. It consists of 2 elements that unite at the clavicle in dogs. In dogs the caudal part, known as the cleidobrachialis, runs from the clavicle to the humerus and is closely associated with the deltoid. The cranial portion runs from the clavicle to various attachments via a broad aponeurosis on the upper part of the head and neck. It is called the cleidomastoideus in the dog because it inserts on the mastoid process of the temporal bone. It may have a different name, like cleido-occipitalis, in other mammals. The name brachiocephalicus signifies that this complex of muscles runs from the upper arm to the head and does not specify the details of muscle attachments because these vary so much from species to species. The brachiocephalicus advances the limb and may also extend the shoulder joint, but this depends on the cranial attachment being fixed and the limb being free to move. However, when the forelimb is firmly on the ground and the head is free to move, it forces the head and neck either ventrally or to one side depending on whether or not both muscles act in tandem skeletal muscle organ, vertebrate