188

the skull, the rhinal chambers are exposed (as in Pl. LXIII. fig. 1,14,n). These, in
transverse vertical section, are of a triangular form, the apex being formed by the
bases of the prefrontals where they coalesce with the presphenoid. Each prefrontal
divides into an inner or 'medial' and an outer or 'lateral' plate. The lateral plates
diverge and bend upward and outward, forming the side-wall of the rhinal chamber,
from which the turbinals (middle and posterior, Pl. LXV. fig. 3, 19) are developed; the
medial plates coalesce and ascend, forming the rhinal septum (ib.14, and Pl. LXIII.
fig.1, betweem n and 14), expanding above and partly overarching the rhinal chamber,
the main part of the roof of which is formed by the frontals and nasals, with which, how-
ever, a thin layer of the prefrontals seems to be blended as it diverges from the upper
part of the septum. At the upper and back part of the rhinal chamber this layer of
bone (ib. 14) is perforated by numerous minute foramina leading to fine grooves which
radiate to conduct the olfactory nerve-filaments to the pituitary membrane.
This 'cribriform plate' is a peculiarity in which the Dinornis participates with the
Apteryx: in birds generally the olfactory foramen is single on each side; sometimes
they are blended into one. Cuvier called the combined neurapophyses and sense-
capsules, which chiefly form and occupy the rhinal chambers in birds, by the same
name which anthropotomists had given to those parts in Man. He rightly determined
the bones marked 15, 15, Pls. LXII-LXV. to be 'nasals,' but those external to them and
next the orbit might be either 'anterior frontals' or 'lacrymals'. Cuvier inclined,
however, to adopt the latter homology2, but for a reason which is rebutted by the
marked development of the 'posterior frontal'( Pls. LXIV. & LXV. fig.1, 12) in the
Dinornis.
The phenomena of development lend no help to the determination of this question;
the same spread of blastema, between and expanding transversely in front of the eye-
balls, becomes the seat of the histological stages which issue in the bones (14,15,73) prior
to their mutual confluence in Birds. I doubt if I should have been able to settle this
matter, which to some now appears so obvious, if I had not been guided by the light of
general homology. That showed me first what was the essential and constant, what the
secondary and superadded, growth of the bones call by Cuvier 'frontaux anterieurs'
in the Fish and Reptile. The determination of the neurapophysial parts of these bones
in Pisces and Reptilia led me to recognize their homologues in all the groups (Batrachia)
Aves, Mammalia) in which Cuvier and other anatomists, up to 1844 held the 'anterior
frontals' to be absent, or to be represented by the lacrymals. Cuvier was unacquainted

His able coadjutors and editors, F Cuvier and Laurillard, retained this opinion: "Les os externes et plus voisins de l'orbite seraient presque comme on le voudrait, ou des frontaux anterieurs ou des lacrymaux"
(Lecons d'Anat. Comp., ed. 1837, tom. ii. p. 580).
"Ce que pourrait faire croire que c'est le frontal anterieur qui manque, c'est que dans les
oiseaux il n'y a point de frontal posterieur et que le paroi anterieure de l'orbite, a l'endroit ou le frontal anterieur se trouve ordinairement, est manifestement formee en grande partie par une lame transverse de l'ethmoide" (ib.).