OF THE MARSIPOBRANCH FISHES. 
417 
Crocodile (see “ Challenger .Reports,” vol. i., part 5, plate 3, fig. 6, mk .; plate 9, fig. 
5, mk. ; plate 10, fig. 6, mk. ; and plate 11, fig. 2, mk. ; also Trans. Zool. Soc., 1882, 
plates 63, figs. 7, 8 ; 65, figs. 3, 8 ; 66, fig. 5). 
Moreover, I have recently made a large number of preparations of the visceral arches 
of embryo Mammals—Edentata, Insectivora, Rodentia, &c.,—and in these I find a still 
more developed basal rudiment to the primary mandibular arch, namely, a large, 
well-formed terete rod, lying on the symphysis of the “ rami,” and well marked as a 
true “ basi-mandibular.” 
Now, considering the morphological feats performed by these Marsipobranchs, notably 
the two distinct “ intertrabeculse ” of the Myxinoids, and the marvellous develop¬ 
ment and sub-division of the basi-hyal, I think it is not a great extravagance on 
the part of Professor PIuxley and myself to ask them to show one “ sign” more, and 
give us three distinct, rudimentary, distal mandibular elements. 
I shall simply call them median and lateral distal mandibular cartilages ( in.d.m., 
l.d.m.), and leave their deep or superficial nature an open question. 
Like the annulus they have no existence in the Ammocoete, but this is true, also, 
of the fore half of the subocular arch, and of all the hyoid arch. 
It is evident that the Petromyzine type of skull is a great and important modifica¬ 
tion (metamorphosis) of the Myxinoid, for the larval Lamprey represents Myxine, just 
as the larval frog represents the Lamprey. 
But the enormous development of the lower lip in the Lamprey has affected the 
jaws, half aborting them, and the hyoid arch, also, in its upper part, and causing its 
basal part to undergo extreme hypertrophy. The hyoid arch presents fewer difficulties 
than the maxillo-mandibular, but there are some remarkable modifications of this 
region, which are, however, greatly elucidated by what we see in the “ Anura.” It 
has no “ pharyngo-hyal ” element; nor has the Tadpole, at first; its distal part, which 
becomes the “ columella auris,” does not appear in our Common Frog and Toad until 
two or three months after metamorphosis (see my 2nd Paper “ On the Batrachian 
Skull,” pp. 622-624)—a fact discovered by Professor Huxley. But th q position of the 
“ epi-liyal ” region of the hyoid arch, and its continuity with the back of the pedicle and 
pterygoid, is only explicable by reference to transforming and transformed “Anura.” 
The large broad “ epi-cerato hyal ” of the Tadpole is articulated to a special facet 
by a special condyle below the ethmoid in the antorbital region, and it is only after 
the swinging back, so to speak, of the quadrate region that the epi-hyal point is 
carried under the exit of the facial (its own ) nerve (see in Pseudis, “ Batrachian Skull,” 
Part III., Plates 11, 12); this position is a good landmark, and shows that the quadrate 
of the Lamprey should have been post-orbital. 
The epi-cerato hyal (Plate 18, fig. 5, hy., c.hy .; and Plate 19, figs. 1-3, e.hy.) grows 
out from the back of the pedicle and pterygoid (pd., pg.) at a right angle ; a pro¬ 
jection, the beginning of this part, is seen in the Ammocoete (Plate 19, figs. 4, 5, pd.). 
In the adult stage, in some Tree Frogs ( Acris Pickeringii and Phyllomedusa bicolor) 
