_Description._—The sternum is a quadrilateral, curved plate with processes projecting from each angle and from the middle of the anterior and posterior borders. The posterior medial projection, or _metasternum_, is the longest, and has a tall, plate-like ridge—the _sternal crest_, _crista sterni_—running along its ventral surface. The crest serves the important function of increasing the bony area for the attachment of the powerful muscles which move the wings. The anterior medial projection, or _rostrum_, is short, and pierced at its root by an opening from which extend two elongated, saddle-shaped depressions into which the end of the coracoid bones are received. The plate-like process of bone, the _posterior lateral process_, which projects from the caudal angles of the sternum soon divides into two parts. The shorter of these, the _oblique process_, broadens toward its free end and covers the sternal segments of the last two ribs. The sides of the sternum are thus provided with an external and an internal process forming an _external_ and an _internal_ notch. These notches are bridged over by a broad ligament, to which the muscles are attached. In poor flyers, as the domestic fowl, these notches are large. The posterior end of the sternum is called the _xiphoid process_ or _processus xiphoideus_. Anteriorly the sternum is provided with lateral external processes, the _costal processes_. The lateral borders of the sternum are pitted by four depressions into which the sternal segments of the ribs are received. The dorsal, or inner surface of the bone is pierced by openings by which the air-sacs communicate with the interior. THE APPENDICULAR SKELETON The appendicular skeleton consists of the shoulder girdle, the fore limb, the pelvic girdle, or hip bone, and the hind limb. The shoulder girdle consists of the scapula, the coracoid, and the clavicle. The fore limb consists of the arm, forearm, and the hand. The arm consists of the humerus, the forearm of the radius and the ulna; and the hand consists of the carpus, the metacarpus, and the phalanges. The pelvic girdle consists of the ilium, the ischium, and the pubis. The hind limb consists of the thigh, the leg, and the foot. The thigh consists of the femur, and the leg consists of the tibia and the fibula. The foot consists of the metatarsus and the phalanges. THE SHOULDER GIRDLE The shoulder girdle consists of the scapula, the clavicle and the coracoid. =The Scapula.= _Location._—The scapula (Fig. 11, _A_, _B_) lies on the outer and superior rib surface, extending parallel with the dorsal vertebræ.