216 MR. W. K. PARKER ON THE STRUCTURE AND 
ossified by the corresponding opisthotic centres, and made to serve as a rim to 
the cochlea.* 
Seen obliquely from the outside (fig. 5) there is, above and in front, the shell-like 
prootic plate (pr.o’.), and below it a similar, but lesser wing-like growth of bone. The 
cochlea, (ch/.) is also crested, the crest running forwards into a sharp point. A notch still 
persists where the two bony centres meet in front; below that notch the canal for the 
facial nerve (VII.) is seen at both ends, and below and outside its foramen of exit 
(stylomastoid) a thick, hooked club of bone runs across between and outside the 
two fenestree—fenestra ovalis, and fenestra rotunda (/%.0., f7.); the clubbed part is 
the stump of the epihyal (e.y.) confluent with the capsule. 
The anterior canal (a.s.c.) shines through the thin bone, and the posterior and 
horizontal canals (p.s.c., h.s.c.) project from the surface of the opisthotic region. 
On the inside (fig. 4) the anterior canal stands out as an elegant arch over the deep 
and large floceular recess, which is bounded behind by a sharp crest of bone inside 
which is the common sinus of the anterior and posterior canals. Three convexities 
are seen below the recess; these are, from before backward—the ampulla of the 
horizontal canal (/.s.c); that of the anterior (a.s.c.) and the third rising is formed by 
the vestibule (v).). Below these mammillary risings the great porchway for the 
auditory nerve (VIII.) and the bridge over the facial (VIT.) are shown; and there is a 
small tube behind, on the edge of the capsule: in front of these foramina the coils of 
the cochlea are partly hidden by the limbation of its margin, running into the 
anterior sharp process, 
The small, strong annulus (figs. 6, 7, a.ty.) quite enclose an oval space, although the 
crura do not coalesce; the hinder crus has a broad, bilobate end, which overlaps the 
somewhat pointed end of the front crus, and from the outside (fig. 6) partly hides the 
manubrium mallei (mb.). The fore part of the annulus projects, being also dilated 
considerably ; below, and at both ends, the outer face is convex ; the upper crus is 
ridged and grooved below the ridge. On the inside (fig. 7) there is but little con- 
cavity ; this is for about a third of the inner rim, in front of the sharp groove on which 
the processus gracilis of the malleus (.gr.) lies. 
That process is styloid, slightly decurved, and diverges from the manubrium, which 
runs straight along the long axis of the elliptical space formed by the annulus for the 
membrana tympani; it traverses three-fifths of that axial line; and is very slender 
and straight, with a gently bulbous free end. The neck of the malleus (m.) is flat, 
and rises suddenly into the rounded head, which is confluent with the head of the 
incus (7.). Half-way down below the condyloid region the bone projects as an obtuse 
* There is nothing new in the morphology of the skull; in the Frog each of the three great lateral 
bony centres that harden the chondrocranium takes up both a sensory and a cranial tract; thus we have 
a “sphenethmoid,” a “ prootico-alisphenoid,” and an “ opisthotico-exoccipital.” In osseous Fishes the 
semicircular canals run far into proper chondrocranial regions, and are ossified by tracts that have a 
double morphological significance—e.g., the ‘ sphenotic ” and the “ pterotic.”’ 
