246 



DISCOVERY REPORTS 



Dorsal fin and posterior dorsal humps 



The dorsal fin varies a good deal in size, and its limits are ill-defined so that measurements 14 and 15 

 in Table 3 are approximate only: the fin is always very broad transversely. In some whales it may be 

 sufficiently low and broad to merit the old name ' hump ', although ' dorsal fin ' is no misnomer in 

 other individuals (Plate I, figs. 1 and 5). 



Table 5. The external characters of five small foetuses from Horta. See also Plate I, fig. 4 



Along the mid-line between the dorsal fin and the flukes there are from one to six small elevations 

 which may be called the posterior dorsal humps. The old whalemen knew these collectively as the 

 'ridge' (Beale, 1839, p. 24). One hump is always present and is distinguished as a smooth rising of 

 the tailstock just in front of the insertion of the flukes : the other posterior dorsal humps are more 

 abrupt prominences in front of this one (Plate I, fig. 5). In Table 6 the frequencies of the numbers of 

 posterior dorsal humps suggest that among males there may be a normal frequency distribution around 

 four humps, but four, five or six humps seem to be equally common among females. Bolognari (1949) 

 maintained, surprisingly enough, that posterior dorsal humps were absent in all whales (about seven) 

 which he examined in the Mediterranean. Matthews (1938, p. 120) says that in southern whales 'the 

 lesser humps are usually four or five in number. . . . ' 



The posterior dorsal humps do not appear with increasing age, for there is no correlation between 

 the number of humps and the body length, or the degree of physical maturity, or (in females) the 

 number of old corpora lutea in the ovaries. Moreover, Table 5 shows that several humps can be present 

 when the foetus is quite small. 



Table 6. Frequencies of the numbers of posterior dorsal humps in 

 zvhales examined at Horta in 1949 



No. of zvhales 



Females 



1 

 1 

 1 

 3 

 3 

 3 

 12 



