164 MR. W. K. PARKER ON THE STRUCTURE AND 
to the stapes, and the epihyal (ehy.) growing from it; the notochord (nc.) is 
compressed in the middle of the basal cartilage. 
Section 13 (Plate 23, fig. 18).—This partial section is near the last, and shows actual 
fusion of the capsule with the basis cranii (b.0.), and the inferior position of the noto- 
chord (nc.). The lateral band (0.s’.) is not yet continuous with the auditory capsule, 
which is, here, cut through at the meatus internus. The tegmen tympani (¢.ty.), 1s 
severed near part where the short crus of the incus is articulated, and the stapes (s¢.) 
is cut through behind the middle, so that the stapedial artery has been removed. 
The two fenestrae have a convex tract of the capsule between them. 
Section 14 (Plate 23, fig. 14).—The top and bottom of the section are left out, and 
the capsule is drawn with the investing basal cartilage (b.0.). Under this sinuous 
thinnish plate of cartilage the notochord is seen, and above it the basilar artery. 
The crest of cartilage is now the supra-auditory, and the recess outside it at its 
junction with the capsule will be filled in by the squamosal bone. The tegmen 
tympani is cut through behind the incus; but the fenestree (/s.0., fr.) are still in 
view, the anterior and horizontal canals (a.s.¢., h.s.c.) are also seen. 
Section 15 (Plate 23, fig. 15)—The supra-auditory cartilage (s.a.c.) is deficient 
below, where it passes into the supraoccipital. From the great obliquity of the 
capsule we still have the semicircular canals; the anterior (a.s.c.) and the horizontal 
(h.s.c.) are here seen to be imbedded in solid cartilage; part of the vestibule is 
seen below and within. The capsule is separated by a considerable space from the 
basal cartilage (b.0.), which is thick and bracket-shaped; the notochord (n.c.) has 
again reached the upper face of the investing mass of cartilage ; the vagus and glosso- 
pharyngeal nerves (LX., X.) escape through the interspace, right and left, between the 
capsules and the basis cranii; the foramen for the hypoglossal (XII., /: condyloideum) 
has been laid open. These sections of the newly chondrified skull will be better 
understood after I have described the next series. 
Third Stage (continued).—Dissection of the visceral arches of an enbryo Mole; 
3 inch long. 
An inner view of these parts, in connexion with the auditory capsule, is shown as 
drawn from an outspread preparation; the osteoblastic tracts had been removed from 
MEcKEL’s cartilage (Plate 28, fig. 1). The part of the capsule containing the semi- 
circular canals (a.s.c., A.s.¢., p.s.c.) is in its natural relation to the arches, and shows 
their extreme obliquity. The capsule is cut away so as to show the base of the stapes 
(st.) in the fenestra ovalis. That part of the hyoid arch which corresponds to the 
epibranchial 
the epihyal (ey.)—is seen to be outside the stapes, and to be con- 
fluent with the capsule a little above the insertion of the head of the pharyngohyal 
(stapes). The junction of the inturned end of the long crus of the incus (/.c.2.) is 
from the eye in the figure, and is hidden by the base of the stapes, the perforated 
stem of which is at a right angle to that part of the incus. Looking upon the short 
| 
| 
. 
| 
. 
