266 MR. W. kK. PARKER ON THE STRUCTURE AND 
folded meatus externus wedges in between the postelenoid process and the mastoid ; 
the latter is an oval, ear-shaped tract, subconcave below, with a limbate margin, and 
a narrower hole in its inner, proximal part; that hole is the stylomastoid foramen, 
and a small convexity in front of and outside it is due to the fusion, with the mastoid, 
of a small epihyal. 
Behind and within the ear-shaped base of the mastoid process the smallish opening 
for the 9th and 10th nerves is seen. The opening for the 12th nerve, behind, and for 
the internal carotid arteries, further forwards, are very large indeed. Only half of the 
large strongly curved occipital condyles can be seen in the lower aspect of the skull. 
A section of the skull of the adult (Plate 39, fig. 3) shows three convexities along 
the dorsal line: the first long, over the nasal labyrinth; the next somewhat shorter, 
over the front parietal region ; and the third short, over the ear-capsules and hind brain. 
The great septum (p.e.) is ossified over all the proper ethmoidal territory and most of 
the proper septal ; this latter is elongated in front by the partition of the snout (s.z., 
al.n.), which hooks, downwards, in front. From it the recurrent or JAcopsoyn’s cartilage 
(rc.c.) proceeds, scarcely lessened in relative size since birth (Plate 39, fig. 1, re.c.). 
‘The ridge of the perpendicular ethmoid (p.e.), behind and above, forms a very obtuse 
angle with its top in front, and a very acute angle with the axis of the skull, behind 
and below, thus the cribriform plate lies well down in front of the proper cranial cavity. 
The septum bulges downwards in the true olfactory region, and rises again where 
the perpendicular ethmoid passes into the presphenoid (p.e., p.s.); inside that part 
the optic foramen (11.) and sphenoidal fissure (V'?.) can just be seen. The nasals and 
frontals form the wall-plate of the great partition; below, the vomer (v.) has become 
fused with the palatine plates (p.m., pa.) dividing the nasal channels, below. Under- 
neath, the right channel can just be seen, and further back the palato-pterygoid side 
wall (pa., py), and the lip of the tympanic («.ty.) under the Eustachian opening. The 
basis cranii (0.s., 6.0.) is thin and sinuous, thickest behind, where it dips and forms the 
free fore margin of the foramen magnum. But little sella: depression exists inside 
the foramen ovale (V*.). Above, the frontal and parietal (/., p.) form a thinner roof 
than in the young (Plate 38, fig. 7); there is a rudiment of the tentorium cerebelli 
growing from the inner face of the parietal, and from the fore edge of the auditory 
capsule. The arch of the anterior canal (a.s.c.) is well marked, the prootic bone is 
crested, roughly, above it ; below, is the deep floccular recess (fi.7.), and below that 
the multiperforate meatus internus (VIII), and the bridge over the facial nerve (VIL). 
The large openings for the 9th and 10th (IX., X.) and the 12th nerves (XII.) are also 
seen in this aspect. Above, the vertical and transverse ridges of the supraoccipital 
(s.o.) are seen projecting beyond the line of section, which was on the left of the 
middle. 
In front of the auditory capsule the septa between the large air-cells shine through 
the inner table of the squamosal (sq.). 
In the front view (Plate 39, fig. 5) the huge foremost coil of the middle turbinal 
