180 
ME. W. K. PAEKEE ON THE STETJCTTJEE AND 
from a like deposit in the basisphenoidal, whilst, common to both, is the permanently 
separate cortical plate, the “ parasphenoid.” 
The posterior sphenoidal region, like the anterior, is devoid of any distinct bony centre, 
and must likewise be surveyed by the primordial land-marks, the nerve-passages. Thus 
the lines that fall unto it are from the “ fenestra,” in which the optic passage lies in its 
fore part, to the great “ foramen ovale ” behind. Apparently its landmark has been 
removed ; for the “ prootic ” stretches forwards over two-thirds of this space (Plate VIII. 
fig. 9, al.s.,pro.). 
Below, in the basisphenoidal region, and on the sides, as far as they are unaffected by 
the prootics, the posterior resembles the anterior sphenoid in all that is essential ; above, 
however, we note a difference ; for we are now behind the great fontanelle, and the ali- 
sphenoids end above in a roof-plate, a rudiment of the very perfect cartilaginous roof of 
the Shark, in which type the “ fontanelle ” looks forwards at the fore end of the cranium. 
In Osseous Fishes the thick upper edge of the alisphenoidal cartilage adjoining the 
roof is separately ossified, and forms their large “ postfrontal,” the cartilaginous basis of 
which may, or may not, pass across the primary 44 fontanelle.” 
The postsphenoidal roof-plate is feebly ossified by endostosis, the rudiment of a “ supra- 
sphenoidal ” bone. This upper tract is lozenge-shaped, but the posterior and lateral 
angles pass into the adjacent regions (Plate IX. fig. 6, su.s.). 
The outstretched auditory region has acquired one large pair of bony centres, the 
41 prootics ” ( pro.); but the roof-crest ( 4< pterotic the supero-posterior (“ epiotic ”), and 
the infero-posterior (“ opisthotic ”) regions are but little differentiated in this way ; yet 
the auditory masses are largely ossified behind, having a borrowed source of bone, the 
44 exoccipitals ” ( e.o .). 
Seen from the inside (Plate IX. fig. 5), the periotic masses have a smoothly rounded 
face, which, projecting inwards, takes from the cranial cavity (Plate X. fig. 9); outside, 
as in the Lacertians, these masses project so as to increase the breadth of the skull 
threefold, thus throwing out the mandibular pier, and giving the mouth its enormous 
gape. 
In a section made through the 44 foramen ovale ” (Plate X. fig. 8, 5), the ampulla of 
the anterior canal is exposed with part of its arch ; here the parietal (p.) is the only roof 
to the skull in one place, above the posterior fontanelle ( p-fo .) ; externally the fore edge 
of the prootic region (pro.) is rather flat and largely unossified ; this is the part where the 
44 metapterygoid root” has coalesced with the front face of the auditory capsule. This 
narrow outer half of the projecting prootic region is strongly clamped by the supratem- 
poral part of the squamosal ( s.t .). Ossification has affected the rest of the cartilage 
throughout, and it reaches nearly to the 44 posterior fontanelle ” above, and to the thick 
part of the parasphenoid ( pa.s .) below. The 44 Gasserian ganglion” (5) is seen in situ, 
and above it a projecting spur of bone. 
In the next section (fig. 9) the crown of the arch of the anterior canal is cut through 
( a.sc .), and the whole width of the labyrinth-cavity is exposed, near the middle of which 
