24 
MR. W. K. PARKER OK THE STRUCTURE AND 
Broad in front, and rapidly narrowing backwards, they each have four small finger- 
shaped cartilages attached to them, the hindmost of these is confluent with the great 
plate and the rest are merely articulated with it: these are the rudimentary “ cerato- 
branchials ” (c.&r 1-4 .). 
These rays or rudimentary intra-branchial arches lie in the floor of the throat, above 
and within the branchial pouches ; but outside and below these there are four pairs of 
large extra-branchial cartilages ( ex.br 1-4 .) that form most of the framework of the pouches 
and lie close within the outer skin—are, indeed, subcutaneous cartilages, like the 
“labials,” and do not belong to the category of true “visceral arches.” 
The foremost of these remains free distally, articulating with the widest part of the 
hypo-branchial plate ; but the rest have become confluent with it : they all four coalesce 
with each other, above, like their counterparts in the Lamprey’s branchial basket-work. 
The first and fourth of these cartilages are bags or pouches folded into many hills 
and hollows; the two in the middle are widish bars. 
The first and second from their hind margin, and the other two from their fore margin, 
send inward tooth-like rudiments of branchial rays : these agree with the binding parts 
that make the bars into a basket-work in the Lamprey. , 
In the Sharks (see “ On the Selachian Skulls,” T. Z. S., vol. x., plate 38, figs. 1 and 2 ; 
and Gegenbaur’s ‘Selachians,’ plates 11-20) we see that the extra-branchials are 
feeble, the intra-branchials typical, and the branchial rays distinct; in the Skates or 
Bays these fringing cartilages are much dilated externally, and these dilatations are 
articulated together and suppress the extra-branchials. 
The two upper labials (Plate 3, figs. 1-3, u.l.) are but little united of the middle, 
and each has a fenestra in it; on the right side there is a lesser hole. 
The labials of the sucking disk (l.l.) are larger than in the last instance, and this 
corresponds with the fact that this species is very generalised and archaic. 
The spiracular cartilage (Plate 3, figs. 1, 2, sp.c .) is confluent with both the “tegmen 
tympani ” and the “otic process” of the suspensorium. 
When these parts are studied, not only after dissection but also with all their 
enclothing structures, we find that the ordinary Batracliian larva is indeed a kind 
of “ Cvclostomous ” fish, and the Lamprey and this larva mutually explain each other. 
Palatal and lingual aspects and a longitudinally vertical section of the head of the 
largest of these Tadpoles (5 inches long) show many instructive things/" 
In the first view (Plate 1, fig. 3), the inferior arches have been removed bodily, and 
the palate turned upwards; we thus get a view of the horny jaw-plates, the oral 
papillae, the quadrate hinge, the condyle for the hyoid, the inner nares, and the whole 
of the palate up to the faucial region. 
The upper part of this Petromyzine mouth shows not only the principal crescentic 
* Professor Htjxlet (on “ Petromyzon,” Jour, of Anat. and Phys., vol. x., plates 17, 18, pp. 412-429) 
lias served as “pioneer” in tliis part of the thicket; and a cleared space, such as he lias made, makes my 
■work comparatively easy. 
