92 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



On a demonstration specimen of the sternum of an ostrich or other flightless 

 bird note the absence of the keel or carina, the sternum presenting a convex ven- 

 tral face. 



The fore limb of birds is greatly modified as a wing, particularly in its distal 

 portions. The humerus is stout, fitting into the glenoid fossa by its convex 

 head. On either side and slightly distal to the head are prominent projections, 

 the greater and lesser tuberosities, corresponding to the trochanters of the femur. 

 The lesser tuberosity is continued distally into a sharp ridge, the deltoid ridge. 

 This side of the humerus bearing the deltoid ridge is the preaxial or radial side, 

 and it is readily observed that a rotation has occurred so that the preaxial surface 

 faces dorsally in the folded position of the wing. The greater tuberosity is post- 

 axial and bears on its under surface a large hole, the pneumatic foramen, leading 

 into the air space of the humerus. The radius and ulna are typical, the former 

 the more slender of the two, the latter exhibiting at its proximal end a projection, 

 the olecranon process or elbow, here met for the first time. The wrist is greatly 

 altered, consisting of but two separate bones the radiale at the base of the radius 

 and the ulnare at the base of the ulna. The remaining wrist bones are fused to the 

 metacarpals to form the carpometacarpus, consisting of two elongated bones. 

 The metacarpals contributing to these elements are the third and fourth. 1 The 

 second metacarpal is fused to the preaxial side of the proximal end of the third 

 metacarpal where it forms a pronounced hump. From this hump projects the 

 second digit. The third digit is the longest and consists of two phalanges, 

 of which the proximal one is much flattened. The fourth digit is a small projec- 

 tion fused to the postaxial side of the proximal phalanx of the third digit. First 

 and fifth metacarpals and digits are wanting. 



8. The pectoral girdle, sternum, and fore limb of mammals. The pectoral 

 girdle of most mammals is reduced and somewhat modified. Only the mono- 

 tremes have complete pectoral girdles, consisting of scapulae, coracoids, clavicles, 

 and interclavicle (see Fig. 2qD, p. 88). In all of the placental mammals, the cora- 

 coid is reduced to a small process, the coracoid process, the interclavicle is 

 missing, and the clavicles are often reduced or wanting (Fig. 2$E). Conse- 

 quently the pectoral girdle of most mammals consists of the scapulae only, 

 which are correspondingly enlarged and important as places of muscle attach- 

 ment. 



Study the pectoral girdle of the rabbit or cat. It consists of two pairs of 

 bones, the clavicles and the scapulae. The clavicles are small slender bones 

 imbedded in the muscles of the front of the shoulder, and as they are not artic- 

 ulated to the rest of the girdle they generally fall off in prepared skeletons. Iso- 

 lated clavicles will be demonstrated and they will be seen in place later when the 



1 Regarded in some texts, however, as the second and third, and the metacarpal here called second 

 as the first. According to Lillie, Development of the Chick, the embryological evidence strongly indicates 

 that the persistent metacarpals are the second, third, and fourth. 



