OF THE MARSIPOBRANCH FISHES. 
419 
are “ extra-branchials ; ” the first and last are pouches, like the bowl of a spoon, the 
second and third are broad bands. But these have inside them, and growing from 
large hypo-branchials, four pairs of short and slender cerato-branchials, inside the 
arched branches of the main branchial artery (“ Batrachia,” Part III., var. loc.). Also 
in Sharks (not in Skates), outside the rays of each branchial septum there is a long 
band of cartilage, pointed above and pedate below ; there are four pairs of these, 
which are of the same nature as the pouches of the Tadpole and the basket-work of 
the Lamprey (see Trans. Zool. Soc., vol. x., plate 38, figs. 1, 2, e.vs.). In the Shark 
the typically-jointed intra-branchial arches, with their “ rays,” dominate; in the 
Tadpole the extra-branchials; in the Lamprey these latter, alone, exist. The huge 
development of the seven pairs of branchial pouches in the Lamprey, with their 
openings— 2nd to 8 th clefts —carries the fore part of the first pouch away, backwards, 
from the hind margin of the hyoid ; but this is a very slight displacement compared 
to what we saw (Part I.) in the Myxinoicls. 
Each main extra-branchial bar is seen to be behind the corresponding cleft or 
aperture (figs. 1, 2, e.b.a. 1 ' 1 , ex.br d" 7 ); but in the adult, there is an additional bar, in 
front, belonging to the hyoid region, and another behind, enclosing the heart and its 
bag ( ex.hypcd.c.)* These nine pairs of main bars are all united below (fig. 2) into 
one complex cartilaginous {< crate.” The cartilage is of the soft kind. Above, on each 
side, the seven main bars run into each other, being united by a continuous growth, 
attached by fibrous tissue to the sheath of the notochord. Opposite the apertures 
each bar bends inwards, and, above and below, the inbent part gives off a crooked bar, 
both over and under the apertures, These cross bars join the next in front at a con¬ 
siderable distance from the aperture, each being strongly elbowed, and each giving off a 
snag, the one upwards and the other downwards. But the cervicorn character of 
these united bars is increased still further by the development of two snags in front and 
one behind, on each main bar, both above and below the cross bars. Then, both above 
and below, a common headland of cartilage unites the whole together. Nor is this all, 
for the lower marginal band (Plate 18, fig. 2), uniting the main bars below, bends 
towards the corresponding part of the other side, and coalesces with it at its convexity. 
This being done, again and again, there is left a row of small oval fenestrse between 
the junctions— -six in all. But the hyoid part of the basket-work, the “ extra-hyal ” 
{ex.hy.) did not exist till after the metamorphosis (see Plate 25, fig. 8, basket work of 
Ammoccete) and the cross bars of the 1st extra-branchial (ex.-br\) form a loop indepen¬ 
dently of the extra-hyal. This loop, however, sends down, now, an elbowed band, which 
runs into the extra-hyal below its middle. The extra-hyal helps to form the grooved 
and perforated quasi-sternum on the lower face of this great respiratory pharynx (fig. 2, 
ex.hy.) and above its junction with the 1st extra-branchial {ex.br 1 .) runs upwards and 
forwards, and is united with its own arch (epi-cerato hyal, e.liy., c.hy.) over its junction 
* The Tadpole has no gill belonging to either the first or the second arch; therefore its three gill-slits 
answer to the 2nd, 3rd, and 4th gill openings of the Lamprey, whose 1st gill opeuing is the 2nd cleft. 
