EXTERNAL CHARACTERS OF BLUE WHALES 



317 



VENTRAL GROOVES 



The presence of ventral grooves is common to all the Balaenopteridae and their 

 arrangement in Blue, Fin and Sei whales is very similar. In Blue whales they 

 run from a point slightly behind the tip of the mandible back to a point rather behind 

 the umbilicus (see Plate XXX, fig. 3). Laterally they extend round to the shoulders 

 and up to the level of the eye (Plate XXVIII, fig. i) or slightly below it. Here they are 

 very short and one or two run forwards into the corner of the mouth. A few grooves 

 immediately below this run forwards for a short distance along the side of the 

 mandible, but the rest stop short on the lower edge leaving the side of the mandible 

 smooth. The longest grooves are those in the mid-ventral line and it is only these that 



-I r 



17 18 19 20 21 



LENGTH OF WHALE IN METRES 



Fig. 50. Spacing of the baleen in Blue whales. The plotted points represent the spacing of the baleen in 

 individual whales. (Black symbols represent South African whales, and circular ones South Georgia 

 whales.) 



run back as far as the umbilicus. The rest become progressively shorter so that their 

 posterior ends form a line which curves forwards to the axilla. Posteriorly the median 

 grooves may end evenly behind the umbilicus, as in Plate XXX, fig. 3, but there 

 is a certain amount of variation here, for some grooves may extend further back than 

 others, or the posterior ends may be broken up and very indefinite, and sometimes in 

 males there is a median groove continuous with the umbilicus and genital aperture 

 (see Plate XXIX, fig. 3, Plate XXX, figs, i and 2, and Plate XXXI, fig. 4). 



On each side of the genital aperture in females there is often, in addition to the 

 mammary grooves, a varying number of small grooves not more than a foot or two long 



