192 MR. W. K. PARKER ON THE STRUCTURE AND 
in between the small cartilaginous paroccipital and the large condyle, the exoccipital 
(e.0.) is seen, and behind the foramen magnum the crescentic lower edge of the 
supraoccipital (s.0.). 
In the end view (Plate 27, fig. 7) some of these things are better seen ; supplementing 
ihe large, smooth parietals (p.), the great transverse interparietal (7.p., see also fig. 6) 
stretches across the top of the occiput from one prootic plate (pr.o’.) to the other. 
Under and behind that superficial plate the true supraoccipital is seen as a large and 
almost semicircular ossification of the endocranium ; the lower transverse edge of the 
plate is notched over the foramen magnum, and rises, and then falls, outside that arch- 
way. A little cartilage exists at its outer edge, between it and the prootic plate 
(pr.o’.), and this cartilage forms a short arched tract over each exoccipital, and then 
fills in a square space over the notched hind part of the mastoid bone (op.). The 
hindermost projecting part of each squamosal (sq.) can be seen, right and left, away 
from the eye. Around the foramen magnum the crescented exoccipitals, capped, behind, 
by the curious condyles—oval above, grooved, and then transversely lobate ; outside 
the exoccipitals, the small fusiform unossitied paroccipital ridges (po.c.) are flanked 
by the mastoid bone (op.). 
A very instructive preparation was made of the diner face of the skull-floor 
(Plate 27, fig. 8); the nasal labyrinth was largely cut away. The top of the upper 
wall (a/.e.) ends in the short, cartilaginous crista galli (cr.g.); behind this, the top 
of the ethmoidal partition wall (p.e.) and the contiguous part of the cribriform plate 
(cr.p.) are ossified as a trowel-shaped centre, with the handle below. The rest of this 
large, exquisite, double sieve, with its thickened rim, is still unossified. Behind, this 
structure is embraced by the gently concave front margin of the orbitosphenoids (o.s.), 
which now meet in the middle of the skull-floor and there lie upon the presphenoid, 
which they have ossified (see fig. 5). 
They are very narrow planks, bent backwards behind, forwards in front, and with a 
sinuous hind edge, the middle part being the narrowest. The small, oblique optic 
foramen (II.) begins at the inner third, and is behind the middle of the bony tract. 
The posterior sphenoid is as remarkable from this view as from below (fig. 5). The 
alisphenoids (a.s.), with their two foramina (V*., V*.), are about twice the size of the 
orbitosphenoids, they project beyond their basal plate in front as much as they fall 
short behind ; there they are free and pointed; in front, they are rounded and turn 
under to the base of the skull; they are wide apart from the orbitosphenoid, and 
the sphenoidal fissure (V4.) between the two plates is large. The huge basisphenoid 
(b.s.) has a concave fore edge, and convex sides, and then ends bebind in four large sharp 
cusps. The two submesial cusps reach much further backwards than the outer ; 
between these pointed projections, externally, the whole bone is toothed and splintery, 
and is attached to the rough toothed fore edge of the cochlear region of the ear- 
capsule by fibrous tissue. 
In front of the deep lateral notch, the bone, right and left, is gently concave, as 
