DEVELOPMENT OE THE SKULL OE THE COMMON EEOG. 
199 
“ supra-,” “ extra-,” and “ infrastapedials,” At page 759 I have said of the “trabecular 
horns” that they “do not coalesce to form the intermaxillary axis or “prenasal carti- 
lage.” This is quite true ,* for the cornua have coalesced before that rod is developed. 
I did not, however, get a full insight into the formation of the nasal labyrinth from my 
researches into the structure of the Chick ; the huge Tadpole of Pseudis paradoxa gave 
me the true insight. I here make correction of my imperfect and somewhat erroneous 
description of my first stage (Plate lxxxi. figs. 1, 2, p. 759). 
The “first stage” in the Fowl answers to the third in the Frog-embryo, so that the 
parts are already highly modified. The first pair of visceral arches (trabeculae, tr.) are 
by the “ meso-cephalic flexure ” bent over and backwards into the shape of hooks, so 
that two-thirds are seen above (fig. 2) and one-third below (fig. 1). The apex of each 
bar is seen projecting outwards at the part where it has coalesced with the investing 
mass (i.v.) ; this free apex becomes the “ lingula” (Plate lxxxii. fig. 3, l.g.). In front of 
the oval pituitary space a large “ commissure” has tied the two bars together for a large 
space, part of which can be seen from below (fig. 1) ; in this aspect we see the free 
“cornua” which have grown into the “ naso-frontal process” (f.n.) from the conjugated 
part of these bars. 
The pituitary space (py.) soon shortens, and the commissural region rapidly lengthens ; 
the trabeculse, themselves thus united, form the thick base of a large crest, which inter- 
venes (fig. 3, eth ., p.s.) between them and the floor of the membranous cranium; this 
secondary crest is the “ orbito-nasal septum and the roof of the nasal sacs grows from 
its top. The first visceral arch has become widely divergent from the second ; and be- 
tween them an arcuate “connective” (“ pterygo-palatine,” pa.,p.g.) has appeared; it is 
very slightly connected with either bar, and scarcely undergoes chondrification. The first, 
second, and third visceral bars neither coalesce with each other nor with the auditory sac. 
E. Comparison of the Frog with the Mammal. 
If the figures given by Professor Huxley (Elem. p. 143) from Ecker’s work be com- 
pared with my earliest stages, the complete correspondence will at once be seen between 
the human embryo and that of the Frog. 
The “maxillary process” (a) seems, as in the Bird (op. cit. p. 139, fig. 57, F, /), to be 
a small additional arch, but it does not chondrify, and is merely a process of the second 
or mandibular bar, and is developed into the palatine, pterygoid, maxillary, and malar 
bones. 
From the middle of the “ sella turcica” to the end of the nasal septum, the cranio- 
facial base is formed of the first (trabecular) pair of arches ; and if the reader would see 
what these minute threads of soft cartilage may become by metamorphosis and growth, 
he should consult the posthumous work of Dr. Esciiricht on the Anatomy of the Cetacea, 
which has recently appeared under the editorship of Dr. Reinhardt * (plate 2 showing 
the primordial skull of Balaena japonica). 
* “ Ni Tavler til Oplysning af Hvaldyrenes Bygning, udfurte til utrykte Eoredrag af afdiide Etatsraad 
Dr. D. F, Eschricht. Med tilhorende Forklaring.” Copenhagen, 1869. 
