106 “TERRA NOVA” EXPEDITION. 
With the exception of the above structures, the inner portion of the canal was empty. 
The lack of pressure in the meatus enabled the sac-lke tympanic membrane to project 
for 3 inches into its lumen. If the canal had been open to the sea-water, this extreme 
outward convexity would be very difficult to understand. 
The tympanum in Monodon and Phocaena is concave externally, and the meatus 
is open. In the following whales the membrane is known to be convex on its outer 
surface, and it is extremely probable that the meatus is closed in all these cases, 
as it undoubtedly is in the Humpback; Balaena mysticetus and Bb. glacialis ; 
Balaenoptera musculus, B. physalus, B. borealis, and B. acutorostrata; Megaptera 
nodosa and Hyperoodon. It is possible that this condition of the auditory canal occurs 
throughout all the larger Cetacea. 
The tympanic bulla was examined in several specimens and was found to be identical 
in shape with that of the Northern Meyaptera. The species Megaptera novae zealandiae 
was founded by Gray on the ear-bone alone, which was found by him to be shorter 
and more swollen than in JL nodosa. 
After a careful comparison of the identical bulla 
from M. novae zealandiae which Gray * described, 
with those of J/. nodosa Boun., | have been unable 
to find any point of difference between the specimens, 
which could not be amply accounted for by differ- 
ences of age and individual variation. For instance, 
the bullae of the 135 feet foetus were very much 
more rounded and swollen than those of the adults. 
(Plate III, figs. 1-3.) 
A specimen f of the left tympanic bulla of J/ 
H 
lalandii, Fischer was examined and found to be 
Fic. 11.— Humpback : 
diagrammatic 
1876. 
section through the layers of tissue 
which surround the tympanic bulla 
and separate the tympanic cavity 
the pharynx: A, tympanic 
cavity; B, bony wall of bulla ; 
C, fatty tissue; D, yellow elastic 
tissue; E, spongy tissue containing 
air; F, muscular layer of pharyngeal 
wall; G, mucous membrane; H, 
cavity of pharynx. 
from 
exactly like the bulla of Northern specimens of J/. 
nodosa, and those from New Zealand which were 
obtained by me. 
The bulla was surrounded ventrally by two 
distinct coats of tissue, each of which preserved, 
more or less, the shape of the tympanic bone. 
The inner layer (see text-fig. 11, C and D) was 
about 3 inches thick and lay close against the bulla. 
* Gray, J. E., Catalogue Seals and Whales, Brit. Mus., 1866, p. 128, and Proc. Zool. Soc., 1864, 
p: 207. 
The right tympanic and periotic bones described in these papers were presented to the British 
Museum by Mr. Stuart in 1864 (No. 1468, now labelled M. lalandii). 
Turner, Sir W., ‘“ Marine 
Mammals in University Mus. Edinburgh,” 1912, p. 65. 
{+ Specimen in British Museum labelled, “ Left Tympanic of Megaptera lalandii, New Zealand, 
Presented by the Wellington Museum.” 
Turner, W., “ ‘ Challenger’ Report, Cetacea,” pp. 30-31, 
Hector, Sir J., Trans. New Zealand Inst., 1878, Vol. X., page 335, 
