162 



MEMOIRS OF THE CARNEGIE MUSEUM 



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describing. In Plialacrocorax uriJe the ulna is somewhat longer than the humerus, 

 while in this Darter the humerus is considerably longer than the ulna. These are 

 interesting facts. 



In Anhinga anhinga the humerus has a length of about 1 3 centimeters, and it 

 presents the usual double sigmoid curve. This latter, however, is far better seen upon 



a superior view of the bone, rather than upon its 

 anconal aspect. (See Fig. 9.) 



The proximal end of the bone is narrow and 

 elongated, merging with the shaft very gradually. 

 The radial crest is a low, long ridge of uniform 

 height ; while the ulnar crest and tuberosity are 

 prominent and are bent anconad. This creates a 

 deep valley between the true articular humeral 

 head and the ulnar protuberance. The excavation 

 over which the latter arches, and where the pneu- 

 matic openings usually occur in other birds, is very 

 shallow, and indeed so very much so that really no 

 fossa may be said to exist there at all. A marked 

 diffuse excavation exists upon the palmar aspect 

 of this part of the humerus ; this is spread out 

 over a regular area just within the distal half of the 

 radial crest, but joins with a far narrower and some- 

 what deeper strip that bounds the humeral head 

 distad, and lies on the opposite side of the bone 

 to the ulnar crest. All this excavation is power- 

 fully marked in Plialacrocorax. 



The humeral shaft proper is subcylindrical in 

 form, being of nearly uniform caliber for the 

 middle third of the bone. At the distal extremity 

 all the most usual ornithic characters are promi- 

 nent and pronounced. The olecranon fossa is 

 shallow, but the ulnar and radial tubercles jut out 

 very conspicuously, though not as markedly so in 

 proportion as in the Cormorants. 



The ulna has a length of about 11.5 cm. and is 

 moderately bowed from one end to the other. The points of attachments for the 

 quill-butts of the secondary feathers present quite a striking feature, and each seems 



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Fig. 9. Anconal aspect of right hu- 

 merus of Anhinga anhinga. Fig. 10. An- 

 terior view of right femur of A. anhinga. 

 Fig. 11. Right coracoid of A. anhinga. 

 Seen from in front. All drawn in outline, 

 natural size, by the author, from Spec. No. 

 18259, Coll. of U. S. Nat. Museum. 



