520 
Proceedings of the Royal Society 
three or sixty -four, and the formula is CkD 15 or J6 , L 15 Cd 26 , and 
there are fifteen or sixteen pairs of ribs. Balcenoptera borealis is, 
therefore, intermediate in length, in the number of its vei-tebrae and 
of its ribs to B. rostrata on the one hand, and to B. musculus and 
B. sibbaldii on the other. 
The seven cervical vertebrae of niy specimen are all separate bones, 
except that the right lateral mass of the atlas is anchylo'sed to the 
body of the axis. This is an exceptional arrangement in the fin 
p 
whales* and has not apparently been seen in any of the olhet skeletons 
of borealis. The atlas has a transverse process* short, twisted, and 
compressed from before backwards, and a median backward-pro- 
jecting ventral process corresponding with Professor Flower’s de- 
scription of the Leyden specimen. The ring is markedly divided 
into an inferior part for the rudimentary odontoid, and a superior 
rachidian part by a process projecting inwards on each side. This 
character is also well seen in the atlas in the Museum of the College 
of Surgeons, London. The height of the atlas is 10 J inches ; that 
of the axis 13 inches. The extreme transverse diameter of the atlas 
is 14 J inches; that of the axis 2 If inches. The axis has a thick 
spine. The transverse process has a slender upper and a plate-like 
lower limb, which unite externally to form a broad plate-like process 
directed backwards and outwards. The vertebrarterial foramen is 
only If by 2J inches, and is placed near the upper border of the 
process. The rachidian ring is 4f by 3J inches. In the 3rd and 
4th vertebrae the vertebrarterial foramen is completed by the junc- 
tion externally of the superior and inferior limbs of the transverse 
process. In the 5th vertebra these processes are separated exter- 
nally by an interval of 4 inch ; in the 6th, by an interval of 1 J inch ; 
in the 7th, whilst the superior limb is long and curved down- 
wards and outwards, the inferior limb is represented by a mere 
tubercle. In the Leyden specimen the vertebrarterial foramen is 
incompletely bounded in the 2nd to the 7th inclusive. In 
the Berlin and Bergen skeletons only the axis has the foramen 
completely bounded by bone. In the Brussels skeleton only the 
axis and 3rd vertebrae. The ossification is therefore more ad- 
vanced in this region in my specimen than in these other skeletons. 
The flat surfaces of the upper transverse processes are almost 
vertical; those of the lower transverse process of the 6th cervical are 
