THE RIGHT WHALE OF THE NORTH ATLANTIC. 909 
mental. It constitutes, therefore, a marked difference from the Fin Whales, in 
which these vertebre are distinct from each other in the foetus.* I know of no 
observations on these vertebre in the foetus of the other species of Baleena, though 
doubtless they corresponded in their development with mysticetus. 
As the dorsal vertebree were provided with costal articulations, their number 
corresponded with that of the pairs of ribs. The customary number in mysticetus 
was 13, though Escuricut and REINHARDT saw a rudimentary 14th rib in a fcetus, and 
in a young individual only 12 pairs of ribs were present. In the adult bescayensis 
described in this memoir 14 dorsals were seen, which corresponded with the number 
already referred to on page 907 in other skeletons, so that both in its dorsal vertebree 
and in the pairs of ribs this whale differed from mysticetus. 
I have stated on page 907 that the precise separation between the lumbar and caudal 
regions is associated with the position of the most anterior chevron bone, and I have 
regarded that vertebra as the Ist caudal, the ventral surface of the body of which 
articulated with both the 1st and 2nd chevrons, whilst the vertebra immediately anterior, 
which articulated with only half the 1st chevron, is regarded as the 12th lumbar. 
In their great memoir on the Greenland Right Whale Escuricnr and Rernnarpt had 
previously reached the same conclusion, for they said that the 1st caudal can only be 
distinguished from the last lumbar by both its anterior and posterior borders on the 
ventral surface of the body being provided with articular facets for chevron bones. 
The lumbo-caudal formula in mysticetus is Ly;Cdy., in biscayensis L,Cd,, Here also 
is a specific difference, though not of the same importance as the difference in the 
number of dorsal vertebree and ribs in the two species, for the caudals in the same 
species are subject to variations in number in some individuals. In the seven skeletons 
tabulated by True of the vertebre in the American Right Whale, six had the 
formula L,,, and in five the caudals ranged from 23 to 25, the complete formula 
being C,D,,L,,Cd,; to,;, in all 55 to 57 vertebre. In the number and grouping 
of its vertebrae this whale (B. crsarctica of Corr) corresponded essentially with 
B. biscayensis. 
In B. biscayensis and B. australis the head has been regarded as one-fourth the 
total length of the animal, though in this specimen of biscayensis the skull was between 
one-third and one-fourth of the computed total length. On the other hand, in B. 
mysticetus the head is described as one-third of the total length. 
RIs. 
Fourteen pairs of Ribs were present, which corresponded in number with the dorsal 
vertebre. All the ribs articulated with the dorsal spine, either to the transverse 
processes only, or to both the bodies and the transverse processes. Only the 1st pair 
articulated with the sternum, as is customary in the whalebone whales, and the others 
* J found this to be the case in an advanced fcetus of a Balenoptera sibbaldi dissected in 1869-1870, The fretus is 
described in Trams. Roy. Soc. Edin., 1870. 
