THE PECTORAL LIMB 



It should here be noted that whereas the flippers of all other whales 

 are flat, of a shape determined by the disposition of the tips of the 

 digits, and without marked serrations of the borders or uneven pro- 

 tuberances, that of the humpback has numerous sharply defined promi- 

 nences of a warty appearance, as also occur upon other parts of its body, 

 and one of these is' always situated dorsad of the tip of each digit. 



But few remarks can be offered regarding the great variation in the 

 shape of the cetacean flipper. Just as might be expected the extremes 

 in shape are not encountered in the most speedy sorts. In the latter 

 this member is always moderately falcate and moderately pointed, with 

 graceful proportions. We can but presume that the excessively broad 

 flipper of Orcella and the excessively narrow one of Globwcephala have 

 developed in response to some particular need of the animal in question. 



Following the complete abandonment of the land the cetecean carpus 

 lost the synovial character of the joints. At present the rate of manual 

 ossification is much retarded, probably following this loss of synovial 

 articulation, and the cartilages representing the various carpal elements 

 are closely packed together in a flattened mosaic, without movement save 

 that afforded by the elastic character of the tissues. In some sorts of 

 odontocetes complete ossification of the carpal bones appears to be at- 

 tained with age. 



In most sorts, however, it is even slower, and this is especially marked 

 in mysticetes. In adults of the latter the carpal elements are mostly 

 cartilage, while the bony centers are relatively insignificant and sunk 

 within the hyaline substance, reaching the surface of the cartilage only 

 with age. 3 This is in contrast to the situation in the majority of highly 

 modified aquatic reptiles, for in these the carpal bones appear to be as 

 closely packed as possible. 



The homology of the cetacean carpal bones has often been discussed 

 but without any very convincing success, and it is likely that the question 

 can never be settled. Malm (1871) gave it much attention. Briefly, in 

 the Odontoceti the pisiform, or what appears to be this bone, is occa- 

 sionally represented. Besides this there are either five or six elements, 

 or even additional ossicles which are believed to be supernumerary in 

 character, for the number may not be uniform upon the two sides of 

 the same animal. Usually because of their position a scaphoid, lunar 



8 It should be noted that the drawings of mysticete limbs (fig. 36) have been 

 made from mounted specimens in which the cartilage has been replaced by 

 some modelling substance. Hence the cartilaginous elements of the carpus are 

 not individually defined. 



[255] 



