THE RIGHT WHALE OF THE NORTH ATLANTIC. 903 
Plate III. the bones of the so-called B. antipodarum in the same Museum ; he did not 
reproduce the skull of B. brscayensis, for, as is shown in Plate VII., he had access to 
only a few bones of the skeleton. 
' Tympano-petrous Bones.—From the study of these bones in the Cetacea* it is 
obvious that importance is to be attached to their size, form and markings in estimating 
specific characters. The Tympanic bone in Balena mysticetus was massive; in the 
adult it was from 5 to 6 inches long, from 3 to 4 inches broad, and between 4 and 5 
inches in vertical diameter. The outer surface was divided into two unequal convex 
portions, the posterior of which was much the larger, by a long, wide and deep oblique 
groove ; from its upper border a lip-like process, bounded behind by a groove, projected 
for the attachment of the malleus; the lower part of the outer surface showed a shallow 
concavity and ended inferiorly in a strong keel, which extended the length of the bone 
(Plate ITI. fig. 11). The inner surface was convex and striated with vertical grooves ; 
its upper border was almost horizontal, moderately thick as compared with the same 
border in Balzenoptera, and was rounded into the tympanic cavity, its anterior end was 
slightly notched for the Eustachian tube (Plate III. fig. 13). 
The description of the tympanic in B. biscayensis is based on the examination of 
three specimens, which in their general form have the characters of Baleena and not of 
Balznoptera. They varied in length from 52 to.52 inches, in breadth from 32 to 34 
inches, in vertical diameter from 42 to 44 inches; in all, the height was greater than 
the breadth. B. biscayensis differed from mystecetus in the anterior division on the 
outer surface being more rounded, in the lip-like process from the upper border being 
defined behind by a deep notch and not by a short groove, in the postericr border 
_ being more rounded and less ridge-like than in mysticetus, in the anterior border being 
more gently continued into the keel and the junction not being almost rectangular as 
in mysticetus, in the latter of which the keel was prolonged further forward (fig. 10). 
The striated part of the inner surface was more flattened in bescayensis, its upper border 
was thinner and more oblique, and it terminated anteriorly in a distinctly deeper 
Kustachian notch than in mysticetus (fig. 12). 
When compared with two tympanics of B. australis a striking resemblance in 
general form with biscayensis was observed. Also in the details of the outer surface, 
in the deep notch defining the posterior border of the lip-like process, in the rounding 
off of the posterior border into the keel, in the obliquity of the upper border of the 
inner surface, and in the depth of the Hustachian notch B. biscayensis and australis 
closely corresponded, though the striated part of the inner surface in australis was 
not so flattened as in biscayensis, and its upper border was relatively thin (fig. 14). 
In all the essential characters, therefore, the tympanics of these animals were practically 
alike. In the genus Baleena the height of the tympanic was materially greater than 
the breadth, whilst in Baleenoptera these dimensions were almost equal. 
* I may refer to my recently published volume, Marine Mammals in the Anatomical Musewm of the University 
of Edinburgh, London, 1912, for observations on and figures of the tympanic bones in many species of the Cetacea. 
