70 MR. W. K. PARKER ON THE STRUCTURE AND 
This takes up three-fifths of the large palatines, the remaining part merely helps 
to wall in the great naso-palatine canal. Each bone diverges backwards and leaves 
an interspace wider than each bar, at the top of which, on the inner side of each, the 
palatine bone is seen to clamp the basis cranii by a dilated plate. 
Then the pterygoids (pg.) begin ; they run forward, a little, inside the palatines, 
and these, in turn, run backwards outside them, fastening together, obliquely. 
Each bone has, away from the eye in this view, an upper plate embracing the 
skull, a flange, as in the palatines—which runs on to the last fourth of the basi- 
occipital (b.0.). Up to the spheno-occipital synchondrosis (b.s., b.0.), the two ptery- 
goids form the margin to a lanceolate space, the sides diverging and then converging ; 
but in their last third the pterygoids diverge again, and then their upper plate is well 
seen. At their middle these bones spread out, sloubling their breadth and becoming 
rugged and notched ; they thus form an angle which wedges strongly in between the 
innermost part of the squamosal and the foremost part of the annulus tympanicus 
(sq., a.ty.). In the angle, here, the foramen ovale (figs. 1 and 9, V*.) is seen. At 
their rounded ends, which are cut away somewhat, externally, the pterygoids are 
capped with cartilage, as in the embryos of most of the lower Eutheria, which have 
this sign or remembrance of the great pterygo-quadrate bar, or endoskeletal upper Jaw 
of the Ichthyopsida. 
The double sphenoidal region is largely displayed in this view ; outside the 
unfloored part of the palatines, the orbitosphenoids and optic nerves (0.s., I.) are 
seen, and behind these a large, lozenge-shaped tract of each alisphenoid (al.s.), behind 
the sphenoidal fissure, through which both the Ist and 2nd branches of the 5th 
nerve (V'*.) pass. Opposite the junction of the pterygoids and palatines there is a 
semi-oval tract of cartilage, separating the presphenoidal region from the basi- 
sphenoidal bone (p.s., b.s.), for here the orbitosphenoids (0.s.) meet and coalesce, and 
the cartilage has, necessarily, a convex form at their junction. In front, where it 
runs on over the hard palate, it becomes the unossified perpendicular ethmoid (fig. 7, 
p.e.). The large, and unusually long basisphenoid (b.s.) has a small pituitary hole 
at its front third, and is longer, contrary to rule, than the basioccipital, that is, 
measured along the mid-line.* 
This is correlated with the great length of the pterygoid bones (pg.), which are one- 
third the length of the bony cranio-facial base, and even in the Unau (Plate 9, fig. 1) 
are only one-fourth, with its relatively much shorter skull. The external descending 
ridges of the basisphenoid (b.s.), like those in the Unau (Plate 9, fig. 1), are hidden 
by the junction with those of the backwardly extended pterygoids. Only the pre- 
pituitary part of the basis cranii is convex along the middle, in the notochordal region ; 
* In the Unau at the same stage (Plate 9, fig. 1) the basisphenoid is one-third shorter than the 
basioccipital ; here the bony basal tracts, measured along the middle in my younger specimen, are as 
follows :—presphenoidal region 2 millims.; basisphenoidal 4°5 millims.; basioccipital 4 millims 
