motion closely imitates the movement of the natural ankle, and this joint is desirable for light work and short, tender stumps. Notwithstanding it is more complicated than any of our other styles, requiring more care and attention, there are hundreds of people using it with such comfort and satisfaction that under no circumstances whatever could they be induced to use any other. No. 216, on page 40.
Double Ball-and-Socket Ankle Joint
This joint is a unique invention, and the idea of its construction was suggested by the single ball-and-socket joint. It consists of two polished glass balls plying in sockets of fibre. There is no substance that could be used for this purpose that presents a harder, smoother surface than glass, and when in the shape of solid polished spheres, plying in perfectly fitted sockets, they are practically indestructible; there is no such thing as wearing them out. A linked steel rod and a back and front tendon securely connect the foot and ankle. The tendons, also the rubber springs, are the same as used in all of our legs, and are applied in the same manner. This is a somewhat lighter joint than the army and navy joint and is recommended for persons of light or medium weight. No. 217, on page 40.
Army and Navy Ankle Joint
The axis of this joint consists of a hollow steel bolt securely fastened in the foot with two vertical rods with nuts at the lower ends. The bolt is stationary in the foot, the ankle working on the upper surface of the bolt, leaving no possible chance for an accumulation of any grit or dirt, thus making a self-cleaning joint. The steel rod, together with the front and back cords, connects the foot and the ankle. Provision is made for
