16 
Proceedings of the Royal Society of Edinburgh. [Sess. 
in front of the posterior pedicle was at first concave, then somewhat elevated, 
and was succeeded by a narrow, deep groove, which formed the posterior 
boundary of a strong curved process. I have elsewhere * named this process 
lip-like or mallear, for the malleus was fused with it ; it ascended towards 
but did not touch the under surface of the labyrinthine part of the petrous, 
and ended in a free rounded edge (fig. 3, l). At its front was the wide 
groove-like depression which separated the posterior from the anterior part 
of the outer surface of the tympanic. The upper border of this part of the 
surface was connected by a broad anterior pedicle *j* to the pre-otic division 
of the petrous. The labyrinthine or proper periotic division of the petrous 
was relatively small ; it lay between and gave origin to the pre-otic and 
opisthotic divisions of the bone, and it formed the roof and inner wall of 
the tympanic cavity (fig. 3, L). 
The gap between the anterior and posterior pedicles, the sinuous border, 
and the edge of the labyrinthine roof had without doubt been associated 
with the membrana tympani, and through the large part of the gap 
behind the lip-like process the sac-like prolongation of this membrane had 
projected into the lumen of the meatus, the wall of which had been attached 
to the margin of the gap. 
Buchanan, in his Illustrations (op. cit.), figured dissections of the dilated 
tympanic end of the meatus in Balcena mysticetus, and showed the sac -like 
surface of the tympanic membrane, which formed a convex projection into 
its lumen and was enclosed by its wall. He stated the sac to be divided 
internally into a major and a minor concavity by a valve-like membranous 
process from the wall, to the whole length of which the slender process of 
the malleus was attached, whilst the handle was connected with the outer 
edge of the osseous tympanum. Buchanan adopted the view of Sir Everard 
Home, that the membrana tympani had a muscular layer, to which he 
added a reticulated nervous plexus situated subjacent to the cuticle. 
KnoxJ saw in Balcenoptera rostrata a bag-like projection of the membrana 
tympani projecting into the auditory meatus; he stated that in a foetal 
Balcena mysticetus the membrane, though thick, is not muscular. The 
presence of muscular and nerve fibres in the membrane is not now accepted. 
Lillie, in his excellent description and figure of the membrana tympani in 
B. musculus, showed that it formed a sac, not unlike the finger of a glove, 
about 3 inches long and § inch in diameter, which projected into the dilated 
* Marine Mammals , op. cit. pp. 20, 74. 
t The anterior and posterior pedicles in Balcenoptera rostrata were thin plates of bone 
and were very easily fractured. 
tj; Catalogue of Anatomical Preparations of the JVhale, Edinburgh, 1838. 
