444 
MR. W. K. PARKER OK THE SKELETON 
is three cells thick, whilst the hooked rudiment of the pedicle and pterygoid (pd., pg.) 
is two cells thick, with an intercalary cell or two at its bulbous end ; its cells are smaller 
than those of the trabecular bar, but they are only a slight degree behind them in 
development, and there is no segmental line between them. What appears to be such 
a line is due to the difference in the size of the cells in the main and secondary bars. 
The notochord ( nc .) is cut across; the mouth cavity (stomadseum) is very large. 
6th Section (Plate 24, fig. 6, 150 diams.).—This is through the mid brain (C 2 .) and 
the massive Gasserian ganglia (V.) ; the notochord (nc.) is enlarging, and the basal 
bars or parachordals (iv.) are much nearer the notochord than in the last, and they 
are circular in section. Here, right and left, there is a curtain hung across the back 
of the stomadceum (m.), partly dividing it from the archenteron. This is the “ velum 
( vl .), (see also Plate 25, fig. 10, vl.). 
In a partial section, intermediate between this and the last (Plate 25, fig. 2, 300 
diams.), the cartilages (iv.) are further from the notochord, still oval in section, and 
three cells thick in their middle. 
7th Section (Plate 24, fig. 7, 150 diams.).—This is in the fore part of the hind brain 
(C 3 .) and the fore third of the auditory capsules (au.) ; it is in front of the meatus 
internus; the capsules are oval in section, are a little flattened on their inner face, and 
slightly tilted outwards, above. 
This is between the large pre- and y>osi-auditory nerve-ganglia. The narrow terete 
parachordals (iv. ) are midway between the capsules and the enlarging notochord. 
The sjoace below is now pharyngeal (phx.). 
A similar, but partial, section made behind the entrance of the auditory nerve (Plate 
25, fig. 3, 300 diams.), shows that the membranous labyrinth (au.) is covered with a 
thin (single) layer of cartilage cells. Here the moieties of the investing mass (iv.), or 
parachordal tracts, are crescentic, and cleave close to the membranous sheath of the 
notochord (nc.). 
8th Section (Plate 24, fig. 8, 150 diams.).—The hind brain (C 3 .) is becoming smaller, 
for this is at the back of the auditory capsule (au.). Below, between the membrano- 
cranium and the capsule, the ganglion of the vagus (X.) is cut across. Here, also, the 
investing mass is in crescentic sections, cleaving close to the enlarging notochord (nc.). 
Part of a similar but partial section (Plate 25, fig. 4, 300 diams.) shows the relations 
of these parts, and the form of the double row of cartilage cells, right and left. 
9th Section (Plate 24, fig. 9, 150 diams.).—This is a very instructive section, made 
through the first pair of branchial pouches and their openings at the end of the hind 
brain (C 3 .) behind the auditory capsules, but through the vagus ganglia (X.). There 
is still a definite tract of parachordal cartilage (iv.) embracing the notochord (nc.), and 
considerable tracts of the first extra-branchial (see also Plate 25, fig. 8, ex.hr 1 .) come 
into view. On one side the top of the arch is cut through, where it runs in the longitu¬ 
dinal upper band, and the section of that band lies close to, but is independent of the 
investing mass (iv.). Part of the arch, above, is seen on the other side and on both 
