— 125 — 



This horizontal dimension does not decrease so rapidly towards the rear as 

 the vertical extent of the same bones; consequently, behind the 10th chevron 

 bone, here given as the type (these bones being sometimes designated as the 

 inferior spinous processes), they assume a broader and more thickset build, 

 whereas more to the front, where the vertical dimension is more considerable, 

 the tall or slender character is more pronounced. 



The first five chevron-bones show gradually increasing lengths, the 5th 

 and 6th being longest of all, and attaining a height of 41 c.M.. The 7th and 

 8th have nearly the same measurement, the gradual diminution setting in after 

 this. The last three chevron-bones consist of no more than two truncated 

 and rounded bony protuberances, present a stunted appearance, being nothing 

 more in the 19th chevron-bone than a pair of roundish pieces of bone measu- 

 ring 4 c.M. in diameter. 



The ribs (costae); fig. 34, 35 & 36. The number of ribs amounts to 

 16 pairs; this number, according to True (6) is also stated by Gervais for 

 Balaenoptera musculus L., varying according to the former author in European 

 specimens of Balaenoptera physalus L. between 14 and 16 pairs, and in 

 American specimens from 15 to 16 pairs. 



Only the foremost pair of ribs is articulated with the sternum and there- 

 fore represents the only pair of true ribs, whereas the other ribs are free 

 at the ventral end, like so-called false or floating ribs (asternal ribs). 



The following is a table of the lengths of the successive ribs on the 

 left side, measured along the outer arching of the bone: 



1st rib 185 c.M. 



2nd rib 223 c.M. 



3rd rib 288 c.M. 



4th rib 307 c.M. 



5th rib 326 c.M. 



6th rib 328 c.M. 



7th rib 329 c.M. 



8th rib 325 c.M. 



We see from this that the increase in length is very rapid in the first 

 5 ribs, viz. from 185 c.M. to 326 c.M.; the maximum length being attained 

 in the 7th rib. Then follows a gradual decrease down to 220 c.M., being the 



