_Description._—The proximal end is most expanded, and is obliquely truncate for the articular excavation adapted to the ulnar tubercle of the humerus. A short angular process behind the cavity represents the _olecranon_, which is the _processus olecranalis coracoideus ulnæ_ to which the ligamentum capsulare cubiti attaches. On the inner side of the head is the internal tubercle of the ulna and on the external side the external tubercle of the ulna. An excavation is noted on the radial side of the proximal end for the lateral articulation of the head of the radius. On the upper side near the articular part is located the _sigmoid cavity_. The shaft, or corpus ulnæ, decreases in size near the distal end. It is slightly curved, flattened laterally with an internal and an external ridge. The distal end of the ulna is slightly expanded into a _trochlea_ which is sharply convex and articulates with two free carpal bones, the scapho-lunar, or os carpi radiale, and the cuneiform, or os carpi ulnare. The scapho-lunar is placed on the radial side, and the carpiulnare on the ulnar side. The distal extremity of the ulna is provided with a _styloid process_ and on the dorsal side with a _tubercle_. =The Radius.= _Location._—The radius lies beside the ulna with which it articulates at each extremity. At the inferior extremity the articulation is rotary. It also articulates superiorly with the humerus and inferiorly with the os carpi radiale. _Description._—The radius, cylindrical in shape, is more slender than the ulna. The proximal end is expanded, subelliptical, with a concavity for the oblique tubercle and a thickened convex border for articulation with the ulna. This end is provided with the _tuberositas radii_. The shaft, or corpus radii, is slender, subcompressed, and has a slight bend upward from the ulna. A nutrient foramen occurs in this shaft. The distal end is expanded and rather flattened with two grooves on the anconal side for passage of tendons. For articulation with the scapho-lunar the radius is provided with a terminal _transverse convexity_ produced palmad, which also articulates with the ulna laterally. There is a tuberosity on the radial side of the expansion and inferiorly the _inferior tuberculum ossis carpi radialis_ and superiorly a _superior tuberculum ossis carpi radialis_. =The Hand.=—The hand is made up of the carpus, the metacarpus, and the phalanges. The bones of the hand are so arranged as to allow abduction and adduction, or flexion in the ulno-radial plane, movements which are necessary in the outspreading and folding of the wing. Thus the hand of the fowl moves in a state of pronation, without the power of rotation. The carpal bones are so placed between the anterior arm and metacarpus as to reduce the abduction which is necessary to hold and extend the wing, so that the hand or wing be in a fixed position.