350 PROFESSOR OWEN ON THE GENUS DINORNIS. 
the skull, the rhinal chambers are exposed (as in Pl. LIV. 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. LVI. fig. 3, 19) are developed ; the 
medial plates coalesce and ascend, forming the rhinal septum (ib. 14’, and PI. LIV. fig. 1, 
between 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 
Apteryzx: 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. LIII.—LVI. 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 homology?, but for a reason which is rebutted by the 
marked development of the ‘posterior frontal’ (Pls. LV. & LVI. 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 called by Cuvier ‘ frontaux antérieurs’ 
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 
1 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 antérieurs ou des lacrymaux” 
(Legons d’Anat, Comp., ed. 1837, tom. ii. p. 580). 
2 «Ce que pourrait faire croire que c’est le frontal antérieur qui manque, c’est que dans les oiseaux il n’y a 
point de frontal postérieur, et que la paroi antérieure de Vorbite, 4 ’endroit ou Je frontal antérieur se trouve 
ordinairement, est manifestement formée en grande partie par une lame transverse de ’ethmoide” (¢.). 
