36 THE VOYAGE OF H.M.S. CHALLENGER. 



The table shows the dimensions in inches of this bone in different species of Penguin. 



The single phalanx of the third finger is elongated and pointed, and diminishes 

 in breadth from base to apex. It is slightly longer than the first phalanx of the 

 middle finger, so that its extremity reaches beyond the articulation between the first 

 and second phalanges of that finger. Its base is provided with a single articular 

 surface for articulation with the third metacarpal bone, and a small osseous nodule 

 projects upwards from the ulnar margin of the bone beyond that surface. The lateral 

 surfaces of the bone are smooth and flat. 



The dimensions of this bone in different species are given in inches in the table on 

 the following page. 



Comparative Eemarks. 



The skeleton of the Penguin's wing as a whole differs in several particulars from that 

 of other birds. Perhaps its most characteristic feature is to be found in the great 

 amount of compression exhibited by all the bones of the anterior extremity. This flat- 

 tening of the bones has doubtless arisen in accordance with the altered function of the 

 wing in these birds. In the majority of birds the principal function of the wing is to 

 support the bird in, and to propel its body through the air. In the Penguins, on the other 

 hand, the power of flight is lost, and the wing is converted into a paddle which serves the 

 purpose of propelling the bird through the water. In accordance with this alteration of 

 function, the bones of the wing are so modified in form that that organ may be carried 

 forwards while its sharp anterior margin offers the minimum resistance to the sur- 



