350 PROFESSOR OWEN ON THE GENUS DINORNIS. 



the skull, the rhinal chambers are exposed (as in PI. LI V. fig. 1 , i4, n). These, iu 

 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, PI. LVI. fig. 3, i9) are developed ; the 

 medial plates coalesce and ascend, forming the rhinal septum (ib. i*', and PI. LIV. fig. 1, 

 between n and u), 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. u) 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 is, is'. Pis. 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 ' (Pis. 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 (h, is, 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 ant^rieurs' 

 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, Mammaha) 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 03 externes et plus 

 Toisins de I'orbite seraient presque comme on le voudrait, ou des frontaux anterieurs ou des lacrymaux" 

 (Le9ons d'Anat. Comp., ed. 1837, torn. ii. p. 580). 



' "Ce que pourrait faire croire que c'est le frontal ant^rieur qui manque, c'est que dans les oiseaux il n'y a 

 point de frontal posterieur, et que la parol anterieure de I'Drbite, i I'endroit oii le frontal ant^rieur se trouve 

 ordinairement, est manifestement formfe en grande partie par una lame transverse de I'ethmoide" («i.). 



