604 
MR, W. K. PARKER OK THE STRUCTURE AND 
“ epiotic,” and it has the confluent parts in it of the anterior and posterior semicircular 
canals (a.s.c., p.s.c.). 
The rest of the posterior canal, with its ampulla, and the hind part of the horizontal 
canal ( h.s.c .), are enclosed in the opisthotic region (op.), once a distinct bone. 
The am pul he of the anterior and horizontal canals (Plate 42, fig. 3 ; and Plate 43, 
figs. 7, 8, a.s.c., h.s.c.), are enclosed in the large high insulated prootic (pro.) ; all these 
canals being walled in with thin bone, show their elegant curves and swellings on the 
outside. 
The threshold of the great doorway is formed by the basioccipital (b.o.), which also 
forms half of the solid concave floor of the hind skull (Plate 42, fig. 2 ; Plate 43, 
figs. 1, 2, 7, b.o.) the side-posts and threshold all meet in the substance of the single 
transverse emarginate condyle ( oc.c .). 
The unossified top of the superoccipital grows as far forwards as the basal plate 
(s.o., b.o.) ; the latter is a transverse lozenge (Plate 42, fig. 2, b.o.) whose obtuse front 
angle wedges in to the emarginate hinder edge of the basisphenoid ( b.s.). 
On each side, under the suture between the lateral and basal bones, there is a 
mammillate thickening for the attachment of the flexor muscles. 
The 9tli and 10th nerves pass through the edge of the exoccipital close to where it 
has become ankylosed to the opisthotic; the 12th passes out further backwards 
and higher up: the hole behind its foramen is the “posterior condyloid” (Plate 43, 
fig. 2, IX, X, XII). 
The large anterior periotic bone (“prootic” pro.), is in relation below with the 
basisphenoid (b.s.) ; this latter is a very elegant two-winged plate (Plate 42, figs. 2, 3, 4 ; 
and Plate 43, figs. 1, 2, 8, b.s.), each of whose fore-turned wings (“ basi-pterygoid 
processes,” b.pcj.), looks forwards and outwards, and is capped with a long oval cartila¬ 
ginous plate, the counterpart of that upon the pterygoid bone (pg.). 
The bone rises behind the pituitary body into a transverse “ post-clinoid ” wall 
(Plate 43, figs. 1, 2, b.s.,), it is then cupped to form the Sella turcica, and then 
ossifies the trabeculae for a short distance, coalescing there with the feeble para- 
sphenoid ( pa.s.). 
Inside the hind skull (Plate 43, fig. 2) there are two tri-radiate synchondrosial 
tracts on each side; the upper of these divides the periotic elements, and the lower 
by its front ray separates the prootic from the basisphenoid, the hind ray separating 
the opisthotic from the basioccipital, whilst the stem divides the two basal plates. 
Here the skull is figured with cartilaginous lines between the bones; further 
forwards it is made into a lattice-work by cartilaginous bands running along sheets 
of membrane. 
The prootic, a little above its base, has a deep rounded notch in front, where the 
trigeminal nerve (Plate 43, fig. 2, V) passes out; and behind this is the large “ Meatus 
interims,” which is a double within, the facial nerve passing in front, and the auditory 
(VIII) behind. 
