324 THE VERTEBRATE SKELETON. 



of five distinct elements arranged in a proximal row of two 

 and a distal row of three, in the adult only the proximal 

 bones can be clearly distinguished, the distal ones having 

 become completely ankylosed with the metacarpals to form 

 the carpometacarpus. 



The two distinct carpal bones are the radial carpal and 

 the ulnar carpal. The radial carpal (fig. 57, 4) is a small 

 somewhat cubical bone, wedged in between the manus and 

 the radius and ulna. The ulnar carpal (fig. 57, 5) is a 

 somewhat larger, more irregular bone, lying adjacent to the 

 end of the ulna. It is deeply notched to receive the carpo- 

 metacarpus. 



The hand. In the adult bird the hand is in a much 

 modified condition ; only the first three digits are represented, 

 and the metacarpals are all fused with one another and with 

 the distal carpalia to form the carpo-metacarpus. 



The most prominent part of the carpo-metacarpus is formed 

 by the second metacarpal (fig. 57, 7), a stout, straight bone 

 expanded at both ends. The third metacarpal (fig. 57, 8) 

 is a more slender curved bone fused at both ends with the 

 second metacarpal. The first metacarpal forms simply a 

 small projection on the radial side of the proximal end of the 

 second metacarpal. 



The phalanges. The first digit or pollex includes two 

 phalanges, the distal one being very small and bearing a claw. 



The second digit includes three phalanges, the proximal 

 one being somewhat flattened. The third digit has a single 

 small phalanx. 



THE PELVIC GIRDLE. 



The bones constituting the pelvic girdle are not only as in 

 other higher vertebrates ankylosed together forming the in- 

 nominate bones, but are also ankylosed with a series of some 

 seventeen sacral and pseudosacral vertebrae. The acetabulum 

 (fig. 61, 5) with which the head of the femur articulates is 

 incompletely ossified. 



