O 
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MB. W. K. PARKER OK THE STRUCTURE AKD 
form a more gaping space for the “posterior nares;” they are notched behind, and 
have the “ hamular process ” suppressed. 
The squamosal ( sq.) with its crescentic glenoid facet (gif) is seen to run from its 
overlapping jugal part on the jugal to the hinder face of the opisthotic region (op.). 
The postjugal elevation is followed by a pneumatic foramen ( pn.f) which opens into a 
definite air cavity. The semiosseous annulus tympanicus (a.ty.; see also fig. 7) is left- 
on one side ; on the other the capsule is exposed. 
Along the middle, behind the posterior nares, the presphenoidal region (p.s.) is a 
thick roundish beam, quite free from bony deposit. But, laterally, in the fundus of 
the orbit, the roots of the orbitosphenoids (o.s.) are ossified, and the optic nerves (II.) 
are seen emerging. Behind the pterygoid, and opposite the last coil of the cochleae 
(chi.) the basisphenoid (b.s.) is seen to be a short broad tract; the cartilage between 
it and the basioccipital (b.o.) is half the extent of the basisphenoidal bone. Outside 
the pterygoids, the alisphenoid (al.s.) can be seen ; in front of these is the sphenoidal 
fissure (V 1,2 .), and at their junction, near the hind margin of the wing, is the foramen 
ovale for the 3rd branch of the trigeminal nerve (V 3 .). 
On one side the malleus (ml.) is seen stretching the membrana tympani (m.ty.), 
radiating to the annulus, and on the other the cochlea (chi.) and tegmen t} 7 mpani 
(tty.) are seen ; also the two fenestrse ( fs.o . and the large hole behind it). On both 
sides the epihyal and the facial nerve (e.hy ., III. read VII.) are shown, and also the 
passage for the 9th and 10th nerves (IX., X.). 
The occipital arch has a good bony threshold, now, the six-sided basioccipital (b.o.), 
which has one side in the foramen magnum (fin.). The large trilobate condyles (oc.c.) 
have the exoccipital bony centres ( e.o .) creeping round them ; they are still a long way 
from the basal bone, and the cartilage near them is perforated by the 12th nerve (XII.), 
and over this passage there is now one large supraoccipital centre (s.o.). 
The end view (fig. 7) shows how large this bone is, now that the two centres are 
fused together (see in the younger specimen— T. hybridci, fig. 2). The occipital 
cincture, in its upper part, is a large shield of bone and cartilage overlapping the 
opisthotic part of the auditory capsules (op.), with their included posterior canals 
( p.s.c.) seen endwise ; the skull is roofed-in by the parietals (p.), and flanked by the 
squamosals (sq.). 
The sectional vieiv of this older specimen (Plate 5, fig. 6) shows w T hat changes have 
taken place since the first stage (Plate 2, fig. 1); during this time the young have not 
doubled their size. 
The arched line formed by the lower edge of the basis cranii is but little elevated; 
the main part of the internasal septum has almost a straight base. The prepituitary 
part is three and a half times as long as the postpituitary; the thickening of the 
great middle wall (p.e., i.tr.), just in front of the presphenoid, has been caused by the 
flattened and pressed cornua trabeculae ; the rest of the thickening, below, is due to 
the intertrabecula, which is there seen to be a long prochordal tract. 
