764 
ME. W. K. PAEKEE ON THE STEUCTUEE AND 
stroma ( gr.st .), then a deep layer of the larger-celled young connective tissue ( r.st .), and 
below this the epithelium of the palate ( ep.l . ). The aggregation of a thick bed of 
nascent fibrous tissue between the skull-base and the palate and fauces, and the conver- 
sion of the greater part of this mass into bone in a very early stage, is common to many 
of the Vertebrata — for instance, the Ganoid and Teleostean Fishes, the Amphibians and 
Ophidians ; the Lizards show this structure much more feebly. 
The thickened and solidified postpituitary part of the basis cranii shows this super- 
faucial mass — the seat of the “basitemporal” ossifications (Plate LXXXI. fig. 4 ,bt.st.) ; 
the fibrous layer thins out towards the occipital condyle. 
The parts of the primordial skull can now be made out more clearly ; the exoccipital 
lamina (e.o.) is growing upwards to meet its fellow in the superoccipital region ( s.o .), 
and thus enclose the spinal chord. 
Above the meatus internus ( m.i .) the anterior semicircular canal is seen to bulge in- 
wards and to grow backwards ; below and behind the meatus is seen the eighth nerve (8), 
below and in front of it the cochlear elevation ( c.l .) nearing the mid line. The low an- 
terior clinoid elevation (a.cl.) and the high posterior clinoid wall ( p.cl .) are well seen, and 
the notochord ( n.c .) mounting up between the moieties of this wall, which now begin to 
coalesce across their middle ; they do not unite, however, either above or below. A 
thin lobe of cartilage ascends the side wall of the skull outside and behind the posterior 
clinoid wall ; this is the rudiment of the alisphenoid ( a.s .) ; it is connected with the 
periotic capsule by a bridge of cartilage, which arches over the trigeminal nerve (5). 
The internal carotid artery (i.c.) finds its way into the pituitary space ( p.t.s .) through a 
mass of soft fibrous stroma. 
On the outer side of the primordial skull other parts can be seen ; this view is given 
in fig. 5 ; here the facial arches are also shown. The nasal labyrinth developes with 
extraordinary rapidity, so that by the end of the first week all the main parts can be seen. 
Anteriorly the flat trabecular horn has expanded into the alinasal cartilage ( al.n .), with 
its enclosed turbinal or vestibular flap (n.t.) ; behind this is the aliseptal region (al.s.)> 
enclosing the inferior turbinal coil ; and posteriorly there is the aliethmoidal lamina, 
which is continued downwards between the nose and the eye as the anteorbital plate or 
“ pars plana” (pp-)*- Fig. 6 shows a transversely vertical section (12 diam.) through 
the ethmoidal region, immediately in front of the anteorbital laminae [p .p.), which are 
seen to be continuous with the aliethmoidal coil ( al.e .), and to have no distinct “middle 
turbinal ” outgrowth on their anterior face. In this view part of the cartilaginous scle- 
rotic (scl.) is shown, and the section is also made through the middle of the palatine 
bar {pa.). Here is seen the true “ schizognathous ” condition of the palate ; the mouth- 
* The “ pars plana ” is continuous with the rest of the nasal labyrinth in all Birds ; my earlier studies of 
these parts misled me ; and in my paper “ On the Osteology of the Gallinaceae” (Zool. Trans., 1863, vol. v. 
p. 179) I spoke of this plate as being “ autogenous in its cartilaginous state, as well as in its ossified condition.” 
In the paper on the Ostrich’s skull (p. 127 et seq .) this part was described as continuous with the rest of the 
nasal labyrinth. 
