17 
1913-14.] The Auditory Organ in the Cetacea. 
lumen of the auditory meatus, where its somewhat rounded end fitted into 
the cup-like base of the plug of wax. By its opposite end it was con- 
tinuous with the membranous lining of the tympanic cavity. A ligament 
about 1 inch long and 5 mm. broad sprang from the upper part of the 
sac, passed towards the tympanic cavity under the malleo-incal joint, and 
became attached to the manubrium of the malleus. The tympanic sac and 
the ligament were together about 4 inches long.* 
The Tympanic Ossicles are frequently missing in museum specimens, 
and I have carefully looked for them in the bullse of the whales in the 
Fig. 4. — Chain of left tympanic ossicles, tympanic cavity and cleft of Balcenoptera sibbaldi, natural 
size seen from above. A, anterior end of tympanic ; E, Eustachian end of cleft ; Ap, anterior 
tympano-petrous peduncle cut across ; l , lip-like process of sinuous border ; M, malleus with 
two processes fused with anterior border of lip ; I, incus ; S, stapes : their several articula- 
tions are represented. 
University collection. The incus, owing to the diarthrodial joints between 
it and the malleus and stapes being apt to give way, is seldom present, even 
when the malleus and stapes with their firmer attachments have been 
preserved. 
The Ossicles in B. sibbaldi will now be described. The upper end of the 
Malleus consisted of a rounded head with a groove separating it from the 
part of the bone which had on its inner aspect two articular surfaces for 
the incus set at an angle to each other. The diameter of the conjoined head 
and articular part was 16 mm. From the lower part of the head, a process 
descended, 18 mm. long, which was fused in its entire length with the 
anterior border of the lip-like process of the sinuous border of the tym- 
panic (fig. 4). A second descending process, parallel and close to the 
* I have figured in Marine Mammals a similar sac in Hyperoodon. 
VOL. XXXIV. 
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