IS 
MR. W. K. PARKER OK THE STRUCTURE AND 
Behind these parts, in relation to the hinder visceral clefts, four other arches are 
beginning to form. These, the branchials, are still more feebly developed,, never acquire 
an upper element (“ epi-branchial ”), but in their arrest and feebleness are supplemented 
by four pairs of extra-branchial cartilages or pouches ; these I shall describe in the 
developed embryos of the larger species of the genus Rana. 
Until then, also, I shall not describe the other superficial cartilages that are found in 
the Tadpole’s head, viz : that over the “ 1st cleft,” and those so largely forming the 
suctorial mouth of the Tadpole. 
In this early stage the cranial nerves pass over the trabeculae through the membrano- 
cranium. 
Here, if anywhere, we ought to find rudiments of pre-oral arches, if there be any ; 
there are certain things in other kinds of embryos, and even adult forms, that suggest 
such a possibility, but none here.' 5 ' 
At present the mandibular pier has two points of fusion with the trabecula ; the 
hinder of them is the pedicle ( pel .), and the front one the palato-pterygoid bar (ppg.) ; 
the pedicle will be largely absorbed, and the palato-pterygoid enormously developed 
during the metamorphosis of the Tadpole. 
Before passing to the description of the well-developed Tadpole, I must refer again 
to the intermediate stages (ibid., Plate 55, figs. 3, 4, 5). 
On its way to the coronoid region of the mandible, the temporal muscle passes over 
the palato-pterygoid bar, and under a leafy growth of the “suspensorium”—the “orbitar 
process ” (< or.p .). In Bufo vulgaris the apex of this leaf coalesces with the ethmoidal 
cartilage, a rare character. This fact, and its nonconformity with what is seen in the 
Tadpole of the Frog, were pointed out to me by Professor Huxley five or six years ago. 
In other species (even of Bufo) I do not find this very peculiar condition of things, 
but the process itself is well developed, even in the wide-mouthed larvse of the 
“ Agiossa ” (ibid., Plates 56-61). 
In the half-grown larvse figured in my paper (ibid., Plate 55, figs. 4, 5, 5a), we see 
the formation of the “ fenestra ovalis ” as an oblique lateral cleft in the auditory 
capsule ; and of the “ stapes ” as the solidification of the soft tissue left in this space. 
In larvse three-fourths grown ossification begins in the tissue over and under the 
chondrocranium. 
'* Professor Milnes Marshall and the writer, from a consideration of the “segmental nerves” of the 
head, from the development of the month itself and of the lacrymal and nasal passages, and from what is 
seen in various cartilages around and in front of the month, hold to the opinion that there are rudiments of 
at least two , perchance three, pre-oral visceral arches. 
But Professor Huxley and Mr. F. M. Balfour will not see with our eyes, and are not in the least 
satisfied with the evidence which seems so conclusive to us. The Lamprey and the Tadpole are indeed 
great stumbling-blocks; if they represent primordial or archaic forms, and if what we see in other kinds 
bear to be interpreted as specialisations having relation to modification of the oral aperture and its 
framework, the onus probandi will still rest with my talented young friend Marshall and me. 
