19 
1913-14.] The Auditory Organ in the Cetacea. 
-edge of the osseous tympanum, described in B. mysticetus the valvular 
fold of the tympanic membrane as attached to the whole length of the 
gracilis, or slender process. Lillie, again, considered that the only attach- 
ment of the membrane to the malleus in B. musculus was through the 
connection of the ligament to a short process, which he regarded as the 
manubrium, whilst the fused process was the processus gracilis. The de- 
velopment of these processes requires to be studied before their morphology 
can be precisely determined. 
The inner surface of the tympanic bone was separated from the outer by 
the tympanic cavity, the upper internal border of the former surface was thick, 
rounded, and striated, where it turned over into the cavity (fig. 4). This 
border was distant from the sinuous upper border of the outer surface by 
the width of the tympanic cleft, which extended forwards from the posterior 
pedicle to the anterior or Eustachian notch of the cleft. In the whalebone 
whales the cleft was approximately horizontal, though in the genus Bahama 
it had a deep notch at its anterior end.* In the toothed whales the cleft 
inclined downwards at this end and opened by a mouth immediately above 
the anterior end of the inferior surface. The Eustachian tube had not been 
preserved in my specimens. Mr Lillie has been more fortunate, and he has 
described in B. musculus a sac-like prolongation of the tympanic membrane 
through the Eustachian notch into the pterygoid fossa, from which the 
Eustachian tube proper arose as a relatively narrow canal, about one 
foot long, which extended forwards to open into the naso-pharyngeal 
chamber. 
Observations have been made in several toothed whales on the arrange- 
ment of the membrana tympani and its prolongation forwards into the 
sinuses in the cranio-facial bones. Buchanan described and figured the 
membrane in the Narwhal (Monodon) as nearly circular, concave towards 
the meatus, convex towards the tympanic cavity ; the manubrium of the 
malleus was, he said, attached to it. In the University Museum is the 
tympanic of a well -grown foetal Narwhal about 5 feet 5 inches long.j- 
The lip-like process of the sinuous border was prominent, and the gap 
between it and the posterior peduncle was occupied by the dried tympanic 
membrane, which did not bulge outwards towards the meatus. The malleus 
incus and stapes were present. The malleus had been attached to the lip- 
like process, but owing to the fragility of the bone it had broken away. 
The auditory arrangements in the Porpoise ( Phoccena communis) were 
* See the figures in my Memoir on the North Atlantic Balcena biscayensis , Travs. Roy. 
,Soc. Edin ., 1913. 
t Proc. Roy. Soc. Edin., vol. ix. p. 10?, 1876. 
