510 MR. W. K. PARKER ON THE STRUCTURE AND 
But the section of the right side, just a degree further back, is most instructive. The 
large superoccipital cartilage is seen embracing and walling in the great sinus (s.0., L.s.), 
and the periotic mass is severed at the junction of the anterior and posterior canals, so 
that the tube opened here is the ‘common canal” (¢.c.). ‘The posterior non-ampullar 
half of the horizontal canal (/.s.¢.) is opened over the hinder part of the tegmen tympani. 
The promontory is cut through at the fenestra rotunda (pr., fir), and outside this is 
seen the head of the stylohyal; all this long sinuous rod (st.h.) is exposed, and also 
the short ceratohyal (¢.hy.) at its base, where it is seen articulating with the three 
rudiments of the next arch (base and larger cornua of hyoid of Man). 
Reconstruction of the skull at this third stage from the foregoing materials will be 
rendered easier by light obtained from longitudinally vertical sections (Plate XXXITI. 
figs. 2&5). In these the first is made, in the facial region, a little to the left of the mid 
line, so as to give the left face of the septum of the nose ; in the next (fig. 3) the septum is 
cut away, and the left face of the right turbinals exposed. In the first (fig. 2), the brain 
is sketched in outline én sifu; in fig. 5 it has been removed to display the inner wall 
of the cranium. The notochord (zc.) has retired from the posterior clinoid wall, and 
has been buried in cartilage; it still lies, however, nearest the upper surface of the in- 
vesting mass. This may be compared with the like view in the first stage (Plate XXVIII. 
fig. 6). There the basifacial axis scarcely made a right angle with the basicranial ; 
here these parts meet at an angle larger by one half: there the notochord mounted 
above the investing mass; here it has retired, and lies below the clinoid wall. 
The gelatinous space called by Raruke the ‘middle trabecula” is gone, and the 
reduplicated lining membrane of the cranium has formed the “tentorum cerebelli” 
(fig. 2, t.cb.). The huge expansion of the hemispheres (C1*) has hidden the middle 
vesicle (C2), as seen from the outside. Behind the large cerebellum (C3) the occi- 
pital cartilage (s.o.) is seen in section ; and below the rounded margin of the basiocci- 
pital (d.0.) is shown, the tract becoming thinner forwards, and ther much thicker close 
to the pituitary body (py.); it ends above in the overlapping “ posterior .clinoid wall” 
(p.cl.). The pituitary depression is not saddle-like, but is a deep cup, floored by a good 
plate of cartilage. The anterior clinoid wall (a.c/.) is rounded, and belongs to the 
presphenoid; the depression in front of it is for the optic chiasma. The median 
plate rises gently in front of the optic depression, and this higher part for a short 
distance belongs to the anterior sphenoidal territory: it is formed principally by the 
trabecular commissure and crests. The rest of the plate belongs to the perpendicular 
ethmoid and septum nasi; the latter is the longest region and the former the highest. 
The lateral ethmoid (a/.e.) is scarcely seen in this view (fig. 2). Below the pituitary 
body the Eustachian opening (ew.) is seen, in the root of the tongue the ceratohyal 
(ty., ¢-hy.), and ia the substance of the lower jaw the commissure of MECKEL’s carti- 
lages (mh.). 
‘These things and some others are seen in the next figure (fig. 5). Outside the fora- 
men magnum (f.72.) is seen the occipital condyle (0.c.); in front of this the “ anterior 
