2. The worker's arm, a terminal appliance in which outward appearance is not considered. The considerations as to the arm socket and its attachment by a shoulder cap are the same for the two types of appliance. _Attachment and Arm Socket._--The surface over the acromion and clavicle is the only point from which support can be given to an appliance for an amputation through the arm; the attachment is made by means of a shoulder cap. The general shape of this shoulder cap and its attachment by means of a strap passed under the opposite axilla are similar to those described for appliances for amputation through the forearm. [Illustration: FIG. 201.] The larger the shoulder cap the more it extends forwards over the anterior wall of the axilla, upwards over the supra clavicular fossa, and backwards over the scapula, the more secure will be the support. The appliance is heavy and has no support other than the axillary strap. The latter has a tendency to ride upwards against the axilla where it exerts a pressure which may be uncomfortable. This may be relieved by attaching a vertical strap which is buttoned to the trouser belt. [Illustration: FIG. 202.] But although this extensive enclosure of the thoracic region may not hinder the movements of the stump forwards and backwards, it must obviously interfere with the movement of abduction. No doubt this movement is the less important of the two, but we ought to try to preserve it as far as possible. In short stumps we must abandon it. But if the stump is long and consequently has no tendency to escape from the socket, even if this slips down a little, movement may be retained by two methods. The first consists in separating the arm socket from a large shoulder cap, and inserting a joint between (see page 87); but the appliance is then heavy and cumbersome. Moreover, although abduction can thus be easily attained, thrusting and pulling movements require a light appliance, and finally it is impossible to secure rotation. [Illustration: FIGS. 203 and 204.--Shoulder fitting of small extent allowing abduction.] It is possible, on the other hand, by means of the other method, which consists in ending the shoulder cap at a line continued vertically upwards from the thoracic margin of the axilla. If the straps are strong and carefully adjusted the result is better than with the fitting over the scapula, so that this appliance is preferable. We here illustrate a method of fitting the straps which we consider a good one. From the posterior part of the ordinary axillary strap, a Y-shaped branch passes to the upper border of the shoulder cap above and in front of the clavicle, this makes up for the small extent of the enclosure of the shoulder. For the worker's arm a considerable enclosure without any joint is essential, in order to secure stability. The arm bucket, usually continuous with the shoulder cap, is made of leather strengthened with steels.