30 THE VOYAGE OF H.M.S. CHALLENGER, 



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



Species. 



Length of 



anterior border 



of humerus. 



Length of 



posterior border 



of humerus. 



Greatest breadth 

 of humerus. 



Eudyptes clirysocovie, from Tristan, . 



Eudijptes ehrysocome, from the Falklands, 



Eudyptes ehrysocome, from Kerguelen, 



Eudyptes chrysolophus, 



Spheniscus demersus, 



Spheniscus magellanicus, 



Sphenisciis mendiculus, 



Spheniscus minor, 



Pygosceles tceniatus, . 



Aptenodytes longirostris. 



n 



94. 



01 



If 

 If 



H 



n 



n 



2Z 



2* 



H 



H 



ih 



Sesamoid Bones. 



In every species of Penguin two sesamoid bones are developed in connection with 

 the tendons of insertion of the triceps muscle and lie behind the elbow joint. 



Of these bones the external is the larger. It is circular in form, flattened from side 

 to side, and articulates by means of its circumference with the external groove on the 

 posterior inferior extremity of the humerus. 



The internal ulnar sesamoid bone is pyramidal in form, and glides over the inner 

 groove on the inferior extremity of the humerus. The opposed surfaces of the two 

 sesamoids glide upon one another, and over each a portion of the tendon of the triceps 

 muscle plays. 



These bones present a singular resemblance in every species of Penguin, and differ 

 only in size. 



According to Owen,' a single sesamoid bone is developed in this region in the Puffin, 

 in the Swifts, and in certain of the raptorial birds. In the Penguins alone are there two 

 separate sesamoids. 



Tlie Ulna. 

 The ulna in the Penguins is of the same length as the radius. It is destitute 

 of an olecranon process, and is much flattened from side to side. Its upper extremity 

 is provided with a single articular surface, adapted to the posterior of the two larger 



^ Cyclopaedia of Anatomy, vol. 1., Art. "Aves," p. 286. 



