OF THE MARSIPOBRANCH FISHES. 
447 
(iv.) the notochord is exposed both above and below, and rapidly enlarging, carries 
the attenuated bars at their soft ends far out from the mid-line. 
Beneath the meatus auditorius interims each parachordal (fig. 4, iv.) gives off a 
small wing or flap which is continuous with the middle of the infero-internal face 
of the capsule ( au.) ; fore and aft of these flaps there is a considerable chink, or 
foramen lacerum, over which the large ganglionic masses of the pre- and po-st-auditory 
nerves (V., X.) lie. 
The chinks in front of the flaps are bounded by the outgoing pterygo-pedicle 
(pd., pg.). This is, now, a notable narrow wing of hard cartilage, right and left, with 
a broad proximal part, a dilated sub-bilobate terminal part growing forwards and 
downwards, and a narrow arcuate stalk. 
Compared with the recently transformed skull (same Plate, figs. 1-3), we see that 
this is the pedicle, with the pterygoid region free, as in a Salamandrian, but with a 
small bud of the future epi-hyal growing from its fore lobe, behind. 
The olfactory roof (na.) is a broad semicircular plate, convex above and concave 
below, and with the external aperture (e.n.) in the round notch; it is composed of soft 
cartilage. 
The auditory sacs (au.) are reniform with the hilus opening as the meatus interims; 
they are somewhat pinched in on both sides, but most on the inner, and their long 
axis is parallel with that of the skull ; as before mentioned, they are fastened to the 
basal plate by a band of cartilage, right and left—the sub-auditory wings of the para- 
chordals (iv.). The capsule has a small perforation under the Gasserian ganglion 
(fig. 4, au., V.). 
C.— Dissection of a large larva of P. fluviatilis, showing the branchial basTcet-work. 
The preparation here figured (Plate 25, fig. 8) had the superficial parts moved from 
the branchial region, so as to show the whole basket-work of one side, and the heart. 
If this figure be compared with that showing the same parts in the young of 
P. marinus (Plate 18, fig. 1) we shall see the changes produced by metamorphosis 
in this part. Here there is no extra-hyal,* and no extra-pericardial skeleton, but seven 
sinuously-vertical bars, each passing behind a cleft or external branchial passage, 
and each united to its fellow, before and behind, by four longitudinal tracts, the 
whole structure is composed of soft cartilage, now much more consistent, and with 
larger cells, than in the embryo. The cartilage is of a peculiarly light and spongy 
kind, much like that described by me some years ago in the Tadpole ot Dactylethra. 
The cervicorn outgrowths seen in the transformed young are not present; the upper 
connecting band is nearly straight, the lower is formed of a series of small arches, and 
these are placed right and left, back to back (Plate 25, fig. 9). 
The principal bends of the main arches are, inwards, behind each aperture, and 
* The loop of cartilage round the 1st gill-opening is lettered ex.hy. by mistake. 
3 M 2 
