70 ANATOMY OF VERTEBRATES. 



toward tlie palmar aspect. The ulnar end of the ulnar convexity 

 is continued anconad to that end of the ulnar tuberosity. An 

 oblique, longitudinal channel divides the anconal end of the 

 radial tuberosity from an almost longitudinal ridge, which is 

 nearer the middle of the anconal side of the distal end of the 

 humerus ; a similar, but shorter, longitudinal ridge or rising of 

 bone, terminates in the anconal part of the ulnar tuberosity. 

 Between the above almost parallel ridges the anconal surface is 

 nearly flat transversely ; it is traversed along the middle by a low, 

 narrow, longitudinal ridge. Lengthwise the bone is here convex. 

 The differences in the humerus of different birds are seen 

 chiefly in the forms and proportions of the proximal crests ; the 

 radial one in the Columhidce, e. g., is shorter and more produced 

 than in most birds of flight. The humerus in the Swift is very 

 short and thick, with strong pectoral and deltoid processes, and 

 with a trochlear groove on the back of the outer condyle : the 

 proximal processes are still further developed in the humerus of 

 the Humming-bird ; a distinct ulnar sesamoid plays upon the 

 anconal trochlea in both. The pectoral process is much produced 

 and is angular in Tachypetes : also in Sterna where it is deflected. 

 The bone maintains its general ornithic character when the pro- 

 cesses have subsided, with the abrogation of the power of flight. 

 In the Apteryx the humerus is a slender, cylindrical, styliform 

 bone, 1 inch 5 lines in length; slightly expanded at the two 

 extremities, most so at the proximal end, which supports a trans- 

 verse oval articular convexity, covered -with smooth cartilage, and 

 joined by a synovial and capsular membrane to the scapulo- 

 coracoid articulation. A small tuberosity projects beyond each 

 end of the humeral articular surface. The distal end of the 

 humerus is articulated by a true but shallow ginglymoid joint 

 with the rudimental bones of the antibrachium, and both the 

 external and internal condyles are feebly marked. 



The humerus is not always developed in length in proportion 

 to the powers of flight ; for, although it be shortest in the 

 Struthious Birds and Penguins, it is also very short in the Swifts 

 and Humming-birds. In the latter, however, it is characterised 

 by its thickness and strength, the size of its muscular processes, 

 and the consequent transverse extension of its extremities ; while 

 in the Cursores it is as attenuated as it is short, and in the 

 Peno-uins the shaft is reduced to a mere lamina of bone resem- 

 bling the corres})onding part in the paddle of the turtle. In the 

 Rasores it rarely equals half the length of the trunk (thorax and 

 pelvis) ; it equals it in the Argala and Pelican ; exceeds it in the 



