646 
ME. W. K. PAEKEE ON THE STEUCTIJEE AND 
Below (fig. 2), but little is to be seen, for the floor of the vestibule forms the vaulted 
roof of the tympano-Eustachian cavities, and these are largely floored by the leafy ptery- 
goid bones. Between the front and middle lobes of that bone the foramen ovale is 
seen (5) — a huge space when seen sideways (fig. 3). The thick, notched margin of this 
passage is formed, behind, by the prootic (pro.), and in front by the sphenoidal wall (al.s.), 
in which is seen the optic foramen (2), which shows where the orbito-sphenoidal 
region ( o.s .) begins. The hinder part of the epiotic region (ep.) is seen roofing the 
double passage for the ninth and tenth nerves ; from this part to the hind edge of the 
pterygoid the region is opisthotic. 
Above (fig. 1), the elegance of the periotic masses appears ; they form the massive 
piers of the occipital bridge, the keystone of whose arch is an oblong brick of solid 
cartilage (s.o.). But these periotic “ piers ” are of twice the extent of the arch, and they 
spread into rounded lobes far beyond the curving of the upper part, where the semi- 
circular canals are imbedded. The carved work on the top varies ; for whilst the 
anterior and horizontal canals ( a.s.c ., h.s.c.) are simply rounded elevations, the posterior 
canal (p.s.c.) has a sharp (epiotic) crest growing from it, which looks backwards, and 
grows forwards and inwards. 
In front of the anterior canal the prootic sends forwards and inwards a rounded lobe ; 
this is separated by one rounded notch, from the superoccipital and by another from 
another lobe. The inner lobe is separated by synchondrosis from the bony alisphenoidal 
wall (fig. 3, al.s., pro.). The outer lobe is the front part of the tract that lies outside the 
horizontal canal, the “ pterotic ” region, which is concave close to the canal, then 
convex, and then, the bone ceasing, we have the “ tegmen ” running into the “ otic pro- 
cess.” This description of the upper view will be better understood if the eye is made 
familiar with the side and end views at the same time (figs. 3 & 4). 
That part of the periotic mass which is directly connected with the middle ear is 
shown in a separate figure (fig. 7), more enlarged ; it is inverted, and the columella carry- 
ing the stapes is drawn as dislocated and turned over. The squamosal and quadrato- 
jugal ( sq ., q.j. ; see also those parts not inverted in fig. 8) have the tympanic apparatus 
affixed to their outer surface, and the great extrastapedial leaf is imbedded in the 
fibrous “ membrana tympani.” Air finds its way between that leafy growth and the 
bones within, and can pass round the columella, through the opening (formed by the 
“annulus,” the tympanies, squamosal, quadrato-jugal, quadrate, and a ligament, see fig. 8) 
into the vaulted tympano-Eustachian cavity. The fenestra ovalis marks the periotic 
regions, for that which surrounds it in front is the region of the prootic, that which is 
behind the opisthotic (fig. 7). The actual opening (fenestra ovalis) is a small funnel, 
lying at the inner and hinder extremity of an oval trough ; the little, semiovoidal, 
cartilaginous stapes fits accurately into this funnel. The inbent proximal part of the 
interstapedial ( it.st .) fits, by its gently convex condyle, into the gently concave outer 
face of the stapes (st.) ; apparently there is a joint-cavity here. Three fourths of the 
