Arm

The arm is the proximal portion of the thoracic limb in domestic animals, extending from the shoulder to the elbow. It is centred on the humerus, the single bone of the region, around which the muscle masses responsible for limb movements are organised, notably flexion and extension of the elbow as well as stabilisation of the shoulder.

The caudal surface is dominated by the extensor muscles of the forearm, particularly well developed in ungulates, forming the tricipital region. The craniomedial part of the arm contains the flexor muscles and the muscle groups connecting the limb to the thorax.

In humans, the arm is characterised by a greater freedom of movement and a much clearer external separation from the thorax, due to a scapula that is less firmly attached to the trunk and a different orientation of the humerus.