212 MEMOIRS OF THE CARNEGIE MUSEUM 



The humerus presents the usual double sigmoidal curve seen in the humeri of 

 almost all birds. Its shaft is smooth and subcylindrical in form, being somewhat 

 compressed from side to side. The pneumatic fossa is inclined to be shallow and 

 the foramina in it very small; but there are pneumatic openings in other parts of 

 the bone, notably at the distal extremity, where large ones occur upon either aspect. 

 The radial crest or the crista superior is very prominent, being of a triangular out- 

 line, with a thickened border distad. The ulnar tuberosity or the crista inferior is also 

 conspicuously developed, with the tuberculum internum much produced. The caput 

 humeri is elongated and spindleform ; it is separated from a flat tuberous area on the 

 ulnar side of the palmar aspect by a deep transverse sulcus, the sulcus transversus. 

 At the distal end of the bone the muscular grooves are very deep on its anconal as- 

 pect, the ulnar side apparently much raised in consequence. A deep fossa exists 

 both palmad and anconad to the trochlefe. A low ectepicondylar eminence is pres- 

 ent, with deep, circumscribed muscular pits near it on the radial border. No very 

 special resemblance exists between this bone in Fregata and the humerus as it is 

 found in any of the typical Albatrosses. The same would seem to apply to the re- 

 mainder of the skeleton of this limb. 



In the ulna we find the shaft somewhat more cylindrical than it is in the humerus, 

 and presenting but a very slight degree of curvature. It has two distinct rows of 

 papillae for the quill-butts of the secondary feathers, the more prominent row being 

 represented by eighteen of them. The concavities for the trochlese of the humerus are 

 deep with raised edges, but the olecranon process is low and tuberous. Its distal ends 

 present the usual ornithic characters, with muscle-grooves very distinctly marked. 



The radius viewed upon its superior aspect presents for its length an elongated 

 sigmoidal curve. This curve for its distal two thirds nearly agrees with the curva- 

 ture of the shaft of the ulna, when the bones are articulated in situ ; while for the 

 proximal third it is reversed, and here occurs a long, narrow, spindle-shaped " interos- 

 seous space." The radial shaft is more or less cylindrical, smooth, and but faintly 

 marked by muscular lines or ridges. The distal end of the bone is considerably 

 expanded in the transverse direction, and here pneumatic foramina are to be seen. 

 Its proximal head is only moderately developed, and it is the middle third of the 

 continuity of the shaft that possesses the greatest caliber. This latter very gradually 

 diminishes as we approach the extremities. 



Fregata when adult has in its wrist the two usual carpal segments, which, from 

 the high state of pneumaticity they enjoy, are extremely light. Although they have 

 the usual form seen in birds, they are here powerfully marked by the various mus- 

 cular-grooves and articular facets that characterize them. 



