ANATOMY OF BALDEN OPTEEA EOSTEATA. 
253 
The prootic portion resembled a three-sided pyramid, having its apex pointing forwards 
and outwards ; it projected into a cavity in the squamous bone, which was traversed by 
the Eustachian tube and tensor tympani muscle ; its surfaces were rough and somewhat 
tuberculated, pierced by numerous small irregular foramina. On its inferior surface it 
presented a flattened pedicle, the processus anterior mallei, by which it was united to 
the anterior extremity of the tympanic bone. The tympanic portion was united to the 
petrous by the two flattened osseous pedicles just described ; it measured 3-g- inches in 
length by 2 inches in breadth, and 1-|- inch in depth ; in consistence it was extremely 
dense and brittle, and in shape it resembled a Cypraea or Bulla shell * : its upper and 
outer edge formed an extremely irregular extended lip and presented three notches, one 
situated in front of the anterior osseous pedicle of the tympanic bone, which was hollowed 
into a groove, and transmitted the tensor tympani muscle. The second notch was 
placed between the anterior pillar of the tympanic bone in front and a large promontory 
or ridge behind, which was continued upwards into a bony spur, and was continuous 
with the handle of the malleus. This notch was for the entrance of the eustachian 
tube. The third, or posterior notch, was situated behind the prominent ridge before 
mentioned, and in front of the posterior pillar of the tympanic bone ; this was the audi- 
tory meatus, and towards it the fibro-cartilaginous ear-pedicle ran ; in the recent state 
it was somewhat quadrilateral in shape and looked directly outwards. The inner lip 
of the tympanic bone was bullate and rugose; it did no't come into contact with the 
petrous bone, but was separated from it by a small interspace, which in the recent con- 
dition was filled up by the continuation of the fibromucous membrane that lined the 
cavity of the tympanum. 
The labyrinthic segment, which contained the internal ear, formed the roof of the 
tympanic cavity ; it presented four surfaces, viz. superior, inferior, external, and a poste- 
rior. The superior surface was concave, rough, and porous ; it exhibited internally a 
large oval aperture, the internal auditory meatus, whose long axis extended from below 
and without upwards and inwards, it presented internally on its floor two digital fora- 
mina, one small and obliquely placed, the aqueductus Fallopii, which transmitted the 
portio dura ; the other, or larger foramen, was placed posterior and inferior, and termi- 
nated in a conical fossa, which was perforated by an irregular series of foramina [Ma- 
cula cribrosa ) for the transmission of the portio mollis to the internal ear : these fora- 
mina were separated from each other by an osseous ridge. 
Posterior and external to the internal meatus there was a deep funnel-shaped depres- 
sion which terminated in a cul-de-sac, internal to which, and directly posterior to the 
internal auditory meatus, was a small oval tube, which opened into the cochlea, the 
aqueductus cochleae ; the lower or tympanic surface of this portion of the bone was 
convex, hard, and smooth, and its anterior external border was perforated by the aper- 
ture of exit of the portio dura nerve. The posterior surface, which was continuous with 
* A S 00( l representation of this segment is given in the ‘ Catalogue of Seals and Whales in the British Museum ’ 
by Dr. Gray, 1866. 
