148 A BOOK OF WHALES 



van Beneden remarks that it has been found to 

 characterise all the examples of B. borealis that have 

 been examined from this point of view, with the 

 exception of a specimen studied by Sir W. Turner 

 in 1882. 



This state of affairs characterises the two specimens 

 in the British Museum, and therefore the number of 

 ribs allowed in the table on p. 147 must be increased 

 by one. For there can be no doubt that this two- 

 headed rib represents two, as it is articulated with the 

 transverse processes of two vertebrae. As is the case 

 with all Mystacoceti, except Rhachianectes, the first 

 few ribs have capitular processes ; but these processes 

 do not articulate directly with the centra of their 

 respective vertebrae. In B. vmsculus the first three 

 ribs have these processes ; in B. borealis I noticed 

 four ; in B. sibbaldii there were again only three, the 

 last two of which were so much longer that they may 

 perhaps articulate directly with the centra. Professor 

 Delage* has directed attention to the fact that the 

 only rib (the first) which articulates with the sternum 

 does so by two heads ; it is first of all attached by an 

 articular surface, and then by a "pseudo-articular" 

 fibrous surface. This double attachment is, it seems, 

 paralleled in Edentates. 



The sternum of Bal&noptera is usually a somewhat 

 cruciform bone such as is displayed in the figure on 

 p. 44. The cross-like outline is not always so well 

 marked, and differences in the proportions of the 

 limbs of the cross are evident, and are certainly in 



* " Histoire du Balcenoptcra muscuhis? Arch. Zool. Experim., \ 885, p. i. 



