AXATOMY OF MEGAPTERA LONGIMANA. 29 



humerus exposed for 3 inches. The cartilaginous olecranon in 

 the Qb to 66-feet-long B. musculus is 7 inches in height, 9 inches 

 in length at the top. In the 50-feet-long B. musculus, the 

 height is 6 inches along the middle, the length at the top 

 7 inches. The dimensions of the cartilaginous olecranon in this 

 Megaptera were not noted when it was moist, but it was much 

 shorter and narrower than in B. musculus, and now, in the dried 

 condition, it is 4 inches in height and the same in length, and 

 has probably shrunk about 1 inch in both directions. 



The interosseous space of the fore-arm is much narrower in 

 the Megaptera than in B. musculus. At the middle, the width 

 in Megaptera is f of an inch ; in the 50-feet-long B. musculus 

 fully 2 inches ; in the 65 to 66-feet-long B. musculus \ inch less, 

 this probably owing to the greater thickness of the bones. In 

 Megaptera it is rather wider (l^ inch) just below the heads of 

 the radius and ulna, and thereafter remains pretty equable at 

 f inch, lessening to | inch just before the epiphysis of the ulna. 

 In B. musculus it narrows a little towards the elbow, and 

 beyond the middle diminishes gradually by the expansion of 

 the radius, and ceases a few inches from the carpus, the borders 

 becoming flattened for contact of the bones. This flattening is 

 5 inches in length in the 65 to 66-feet-long B. musculus, 2 inches 

 in the 50-feet-long B. musculus, but the actual contact appears 

 to have been for about half of these lengths. In this Megap- 

 tera there is no flattening of the interosseous borders and no 

 contact of the radius and ulna, the shaft of the radius resting 

 on its ulnar side on the forward-projecting part of the ulnar 

 carpal bone. This narrowness of the interosseous space in 

 Megaptera is in part due to the less concavity of the radius, but 

 mainly to the greater curvature of the ulna. The curve of the 

 ulna is on both its borders. A line drawn from the ulnar edge 

 of the humerus to the upper edge of the ulna at the wrist gives 

 in Megaptera a bay 4 inches deep ; in the 65 to 66-feet-long B. 

 musculus, 3 inches ; in the 50-feet-long B. musculus, 24. 



The fore-arm of Megaptera is still more differentiated from 

 that of Mysticetus, in which the bones are comparatively short, 

 the radius broad and flat, and the interosseous space wide. 



7. The Elbow-Joint.— The elbow-joint was diarthrodial, with 

 one large synovial cavity. The cavity was continued on the 



