19 
1914-15.] The Baleen Whales of the South Atlantic. 
lower part formed a broad, shallow, concave surface which sloped down- 
wards to the strong keel. The upper border of the outer surface formed 
the sinuous outer edge of the tympanic cleft and a strong lip-like mallear 
process, I, projected from this border. The inner surface was roughened 
Fig. 4. — Right Tympano-petrous, Balcena australis. Natural size. 
A, anterior, P, posterior border of tympanic ; I, lip-like process for mallear attachment ; 
L, labyrinthine, PR, pre-otic, OP, opisthotic divisions of petrous at their junction with the 
peduncles ; M, head of malleus ; S, stapes ; Au, opening into tympanic cavity closed in living 
head at deep end of auditory meatus by membrana tympani, 
in proximity to the keel, but immediately below its upper border it was 
moderately convex and striated, where it formed the inner edge of the 
tympanic cleft, which was relatively thin as it turned into the tympanic 
cavity. This border was mostly horizontal, but anteriorly it formed a 
deep Eustachian notch. 
