As for the costal cartilages, they are, as a rule, ossified, and receive the name of inferior ribs (Fig. 18, 11), united to the preceding (superior ribs; Fig. 18, 9) by articulation; by the other extremity they are joined to the sternum; the first superior ribs generally want them. Sometimes the last inferior rib becomes connected with the one that precedes it, not articulating with the sternum; and thus recalls the relations of the asternal ribs which we have noticed in our study of the mammals. In the bat, as in birds, the costal cartilages are ossified. THE ANTERIOR LIMBS[5] [5] Consult Figs. 21, 33, 34, 38, 39, 46. The anterior limbs, homologous to the upper limbs in man, are formed, as in the latter, of four segments: the shoulder, the arm, the forearm, and the hand. These limbs, considered in the vertebral series, present themselves under very different aspects, which are determined by the functions they are called upon to perform. They constitute the forepaw in terrestrial mammals; in aerial vertebrates they form wings; in aqueous mammals they act as paddles. In whatever series we study them, we can readily find the relationship of the different parts; it is very easy to recognise the same bones in the upper limbs of the human being, the wings of the bat (Fig. 8) and of birds (Fig. 21), and in the anterior paddles of the seal (Fig. 9) and of the dolphin. [Illustration: FIG. 8.--ANTERIOR LIMB OF THE BAT: LEFT SIDE, ANTERIOR SURFACE. 1, Clavicle; 2, scapula; 3, humerus; 4, radius; 5, cubitus; 6, carpus; 7, thumb; 8, metacarpus; 9, phalanges.] In quadrupeds, the shoulder and arm are hidden, the latter more or less completely, in the muscular mass which binds it to the lateral wall of the trunk; so that the anterior limbs only present; free from the trunk: the elbow, forearm, and hand. The Shoulder In some vertebrates, the shoulder is formed of two bones--the scapula and clavicle; in others of only one bone--the scapula; the clavicle in this case does not exist. =The Scapula or Omoplate.=--The scapula is situated on the lateral surface of the thorax, and is directed obliquely, from above downwards and from behind forwards. We must first recall, so as to be able to make a comparison, that in man this bone is placed at the posterior surface of the thoracic cage; so that if we look at the human thorax on one of its lateral aspects we see chiefly the external border of the scapula; it is the external surface (homologous to the posterior surface of the human scapula) which we see in its full extent when we look on the same surface of the thorax in quadrupeds. [Illustration: FIG. 9.--ANTERIOR LIMB OF THE SEAL: LEFT SIDE, EXTERNAL SURFACE. 1, Scapula; 2, humerus; 3, radius; 4, ulna; 5, carpus; 6, metacarpus; 7, phalanges of the fingers.]