20 
Proceedings of the Eoyal Society of Edinburgh. [Sess. 
In the specimen from Belgic Strait the tympanic ossicles, malleus and 
stapes had been preserved, and the malleus was fused by a pair of processes 
parallel to each other with the lip-like process on the sinuous border of 
the tympanic cleft. 
The Petrous bone consisted of the Labyrinthine, Pre-otic and Opisthotic 
parts. The Labyrinthine was locked between the pre-otic and opisthotic 
divisions. Its upper surface was rough for articulation with the basis 
cranii; the under surface showed a smooth convexity directed to the 
tympanic bulla and cleft ; it formed the inner wall of the tympanic cavity, 
in which was a deep fossa ovalis, with the stapes attached to the fenestra 
ovalis. The inner end of the labyrinthine projected to the cranial cavity 
and contained large canals and foramina for the passage of the divisions 
of the auditory nerve and blood-vessels. 
The Pre-otic was a rough mass of bone 17*8 cm. (7 in.) in its longest 
diameter ; the outer end tapered to a point, the inner end was blunted. The 
Opisthotic was a flattened plate 18 cm. in length, and 12 cm. (4'7 in.) broad 
at its labyrinthine attachment, whilst it narrowed posteriorly to a pointed 
process. These divisions were fused by peduncles to the tympanic bone : 
the anterior peduncle connected the pre-otic to the sinuous border of the 
tympanic cleft in front of the lip-like process ; the posterior peduncle con- 
nected the opisthotic to the posterior end of this border, and was separated 
from the lip-like process by a gap, which corresponded with the deep end 
of the external auditory meatus and the membrana tympani in the living 
animal. The pre-otic and opisthotic had strong articulations with the 
basis cranii. Their general form and relations corresponded in the three 
specimens of B. australis, though the opisthotic in those from New Zealand 
was more massive, but not so wide as that from Graham Land. The 
opisthotic in Balsena, when removed in its entirety from the skull, was 
much shorter than in the larger species of Balmnoptera, in which I have 
seen it to attain a length of 43 cm. (17 in.) and to be of the almost uniform 
breadth of 13 cm. in the greater part of its length.* 
The specimens in the Anatomical Museum, as well as those recently 
presented by Mr Millen Coughtrey, warrant the statement that the follow- 
ing species of Baleen Whales are to be found in the South Atlantic : — 
The Balmnopteridse — Megaptera hoops (longimana), Balmnoptera sihhaldi, 
borealis, rostrata, also B. musculus. 
The Right Whale, Balcena australis, has been associated with the South 
Atlantic since its recognition by Desmoulins in 1822. 
* See my memoir on the Auditory Organ in the Cetacea, and compare B. australis with 
the petrous hone in Balsenoptera, Proc. Roy. Soc. Edin., vol. xxxiv. p. 10, 1913. 
