620 
ME. W. K. PAEKEE ON THE STEHCTUEE AND 
projection of the parachordal cartilage (iv.) in front of the auditory capsule. Now, in 
the Salmon (“ Salmon’s Skull,” plate ii. fig. 5, iv., tr.) the free ends of the parachordal 
bands, or “ investing mass,” look a little inward; hut in the Fowl (Huxley, Elem. 
Comp. Anat. p. 138, fig. 57, F ; “ Fowl’s Skull,” plate lxxxi. fig. 2, Ig.) the terminal part 
of each of these plates looks outwards and is abruptly truncated. 
A line drawn, on each side, obliquely from the front of these processes to near the 
apex of the notochord (fig. 3, nc.) would be the true land-mark separating the trabeculae 
from these hinder bands. The pyriform pituitary space (jpt.s .) is now seen to have a low, 
but sharp wall enclosing it, on this side and on that. This wall is a crest growing 
upwards from the trabecula, and is the simple rudiment of the anterior and posterior 
sphenoidal wings and ethmoid, in one. Where these crests begin to die out, in front, 
there we see a cartilaginous bud on each side of the beginning of the internasal commis- 
sure. This is the first upgrowth of the prefrontal mass or lateral ethmoid. Afterwards 
(see “ Frog’s Skull,” plate v. fig. 3) these buds will coalesce with each other and with 
the lateral crests, so as to form the round fore end and straight sides of the growing 
cranial trough. 
Opposite these buds, above where the concave facet for the hyoid is formed, the 
mandibular pier is bent inwards, and from this concave margin there has arisen a large 
triangular, sessile leaf of cartilage (or.jp.), which is decurrent, for it runs backwards 
along the mandibular stalk, cresting its outer edge. This sessile, broad-based leaf is 
apiculate, and the apex of it has coalesced with the trabecula, just outside the ethmoidal 
bud. This is the “ orbitar process,” which arches over the temporal muscle. 
In the Common Frog (“Frog’s Skull,” plates v. &vi.), the Bull-frog, the Paradoxical 
Frog, and the Aglossal Toads (infra) this perfect arching over does not take place*. 
At present the internasal plate (i.n.'p) is only half as long as the free cornua ( c.tr .) ; 
in front, where the curved bars lie back to back, it has their thickness, but behind it 
is bevelled ; and this thin-edged plate is the commencement of a most extensive commis- 
sure, which will in time, when the larva is perfect, fill in the whole of the pituitary 
space, as in Sharks and Rays. One measure of the extent of metamorphosis undergone 
by these Batrachians can now be given. By my study of the huge Tadpoles of Sana 
jpi/piens and Pseudis jparadoxa f, I learn that the projection from the outer side of the 
cornu trabeculae, which gives attachment to the inner end of the “ prenarial ligament ” 
(p.n.l.), is the rudiment of the “alinasal floor,” which projects outwards in a cervicorn 
manner (Plate 54. figs. 3 & 4) in the adult. 
* Professor Huxley informed me (summer of 1874), after showing me this perfect arch in Tadpoles of the 
Toad I had supplied him with, that he had found, from the distribution of the facial nerves, that the so-called 
“ palato-pterygoid ” of the Lamprey (see Huxley, Elem. Comp. Anat. p. 193, fig. 76, e.) really corresponds 
with the external orbital arch, and not with the true palato-pterygoid. This petromyzine structure, and the 
segmentation of the true palato-pterygoid arcade, make the skull of the Common Toad an object of great 
interest ; further research amongst the “ Bufonidse ” is also suggested, 
t To be given in my next communication. 
