REPORT ON THE SPHENISCID^. 



31 



facets on the lower end of the humerus. The shaft of the bone is triangular in form. 

 Its posterior border is thinner than the anterior, and immediately below the upper end 

 presents a well-defined notch, the prominent inferior angle of which aflfords attachment 

 to the triceps muscle. The jJosterior border slopes obliquely from the notch in question, 

 so that the lower extremity of the bone is much narrower than the upper. The anterior 

 border of the ulna is straight, and is provided at each extremity with a small articular 

 surface for articulation with the radius. The external surface of the bone is concavo- 

 convex, the internal almost flat. The lower extremity of the ulna is provided with two 

 distinct facets, which, however, are continuous with one another. The anterior is convex, 

 and articulates with the upper end of the metacarpus ; the posterior is grooved, and 

 articulates with the ulnar carpal bone. 



The ulna presents the same form in every species of Penguin. In the smaller species, 

 however [Eudyptes and Spheniscus), the upper end of the bone relatively to the lower is 

 broader than in the larger species (Pygosceles and Aptenodytes), and hence in the former 

 the triangular form of the bone is more pronounced than in the latter. 



The table shows the size of the ulna of different species in inches. 



The Radius. 

 The radius is about two-thirds of the length of the humerus. Like all the other 

 bones of the wing of the Penguin it is much compressed. The upper end is provided 

 with a single cup-shaped cavity, which articulates with the anterior of the two larger facets 

 on the lower end of the humerus. Below this surface the anterior margin of the bone is 

 deeply notched, and affords insertion to the fibres of the brachialis internus muscle. Below 



