The medial or costal surface (Fig. 45) is smooth and nearly flat. A shallow furrow (_n_) marks the position of the spine of the scapula. Between the furrow and the coracoid border are two oblique parallel ridges (_o_ and _o′_) for the insertion of muscle-fibres. Near the glenoid border is a well-marked ridge separating the subscapular fossa (_III_), comprising the greater part of the medial surface of the scapula, from the fossa in which the teres major muscle has origin (_IV_). The surface presents several nutrient foramina usually directed toward the glenoid angle. The lateral surface (dorsal surface of human anatomy) (Fig. 44) is divided by the spine (_g_) into two portions. The portion of the scapula craniad of the spine and the cranial surface of the spine bound the =supraspinous= fossa (=fossa supraspinata=) (_I_), while the surface caudad of the spine and the caudal portion of the spine bound the =infraspinous= fossa (=fossa infraspinata=) (_II_). The spine (_g_) begins as a triangular elevated area in the middle of the vertebral margin and runs toward the glenoid angle. It rises gradually for about two-fifths of its length and then the margin becomes broader and the spine remains of the same height to its glenoid end. There is a rough thickening, the =tuberosity= (_h_) of the spine, situated on its free border about midway between the tip of the acromion and the vertebral end of the spine. The spine is inclined toward the glenoid margin so as to form an angle of about 60 degrees with the caudal half of the lateral surface. At the base of the acromion process (_j_) the margin of the spine presents a flat triangular projection, the =metacromion= (_i_), directed toward the glenoid border. The acromion (_j_) continues in the direction of the spine. It is thicker than the spine, smooth and rounded on both its surfaces and both its borders, and its apex is connected by fibrous tissue to the clavicle. The coracoid border (_b_) presents a slight rounded notch, the =incisura scapulæ= or suprascapular notch (_l_), just dorsad of the glenoid angle, and at its ventral end bears the coracoid process (_m_) which is directed ventromediad. The glenoid angle (_d_) is the only one requiring special mention. Between the root of the coracoid process and the glenoid cavity it presents a tubercle, the =supraglenoidal= or bicipital tubercle (_k_), for the tendon of origin of the biceps muscle. The glenoid angle is separated by a contracted neck from the rest of the bone. Between this angle and the inner margin of the acromion there is left a deep notch, the =great scapular notch=. [Illustration: FIG. 46.--CLAVICLE. _a_, medial end; _b_, lateral end.] =Clavicle.= =Clavicula= (Fig. 46).--The clavicle in the cat is greatly reduced. It is a slender curved rod of bone imbedded in the muscles of the shoulder and connected by fibrous tissue to the apex of the acromion process. The lateral end (_b_) is slightly enlarged.