DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
663 
in their passage. Above, these angular and jagged masses show the epiotic eminence (ep.)\ 
formerly (Plate 61. fig. 2) a gentle eminence covered the ampulla and arch of the 
posterior semicircular canal. Looking above (fig. 1) we see that the arches are now 
covered by three bony crests, and the interspaces are dug into deep fossae ; the' whole 
bone being excavated, as in certain Osseous Fishes. The ridge covering the horizontal 
Ganal runs into the epiotic eminence behind ; but in front it runs obliquely outwards as 
far as to the “ tegmen.” This crest overhangs the channel in which the “ portio dura ” 
(figs. 1, 3, 7), which has escaped from the “ trigeminal ” (leaves it at the foramen ovale), 
runs, once more free, along the grooved surface of the bone, to pass over the columella. 
The vestibular portion of the membranous labyrinth runs outwards, and reaches the 
stapes in the postero-superior angle of the extended auditory mass. 
The primary absorption of the cartilage for the fenestra ovalis (Plate 60. fig. 3 
was below, and almost central ; now the oval, funnel-like fenestra is in the centre of 
a thick ring of cartilage ; it looks equally downwards and forwards, and its larger end, 
the prefenestral fossa , is below and in front. The cartilage above the fenestra belongs 
to the prootic region, that below it to the opisthotic ; there is no fenestra rotunda as 
there is no cochlea. Fitting into this auditory funnel is the oval stapes ; its inner part 
is a subconical wedge, its outer part flat ; it is relatively small, but its outer face much 
exceeds that which closes the fenestra. The next part of this truly elegant apparatus 
is like a flute-key, it takes the same direction as the long axis of the stapes, namely 
downwards and forwards. Here let the reader compare the figure (9) with that of the 
auditory chain of the Pig (“ Pig’s Skull,” plate xxxvi. fig. 3, inverting that plate). Here 
there is no interhyal ( i.hy .), and the malleus exists in another form, namely, in the 
mandible ; the stapes, also, has in the Batrachian no fenestrate crest. But the elegant, 
elbowed rod of bone, sticking, limpet-like, to the face of the stapes, and composed of 
two osseous centres, these correspond in both. The upper bone is the os orbiculare ( o.ob .) 
or interstapedial ( it.st .) ; the outer the long crus of the incus (l.c.i.) or the mediosta- 
pedial (m.st.) : one difference there is, and not greater than is seen between Bufo (Plate 54. 
figs. 7, 8) and Pipa, and that is that the discoid part in the Pig is one centre, and the 
long crus another ; here, in Pipa , the discoid part is one with the bar up to the “ elbow,” 
and then commences the other bone (m.st.). The body of the incus (i.) is represented 
in Pipa by a cartilaginous part, not anvil-shaped, but like the leaf of Nymphcea ; and 
the short crus (s.c.i.) is here represented by a strong fibrous ligament. Another shorter 
ligament is seen on the underside of the columella ; these attach the membrana tym- 
pani, “ annulus,” and extrastapedial to the front margin of the stout ring of cartilage 
that encircles the fenestra. If all this structure has an artificial , and as it were manu- 
factured appearance, equally so has the part in which it is set. As in the common 
kinds, the squamosal (sq.) has a descending body and a double head ; the posterior part 
of the head overlaps the tegmen and otic process, and on the anterior part of the head 
the drum-membrane and its ring are attached (see in Bufo, Plate 54. fig. 7). Here 
(Plate 62. fig. 9) the squamosal (sq.) is most carefully moulded over the front and outer 
