226 REPORT—1846. 
in birds. ‘Ce que pourrait faire croire que c’est le frontal antérieur qui 
manque, c’est que dans les oiseaux iln’y a point de frontal postérieur, et que 
la paroi antérieur de J’orbite, a l’endroit ou le frontal antérieure se trouve 
ordinairement, est manifestement formée en grande partie par une lame 
transverse de l’ethmoide*.” But the postfrontal is not always absent in 
birds: it is present as a distinct bone, though small, in the emeu’s skull, 
figured in the ‘ Memoir on the Dinornis’ above-cited ; and it is still more 
developed in the remarkable extinct (?) genus, the immediate subject of that 
memoir. Besides, to anticipate the subject of a subsequent part of this report, 
a parapophysis always disappears from a typical segment of the skeleton 
sooner than a neurapophysis. ‘The rest of Cuvier’s difficulty in the recog- 
nition of the prefrontal in birds was more nominal than real. 
The ethmoid, in the restricted sense in which Cuvier applies the term in the 
crocodile and other animals with divided prefrontals, and in which I would 
apply it in those animals also in which the prefrontals have coalesced, is 
present but remains cartilaginous in the bird. In the mammal it becomes 
bony and contracts anchyloses not only with the still more reduced debris of 
the coalesced prefrontals, but also, in consequence of the change of position 
of the prefrontals through the further progress of concentration, whereby 
they are drawn backwards closer to the prosencephalic part of the cranium, 
and in consequence of the concomitant expansion of the true frontals,—with 
the orbital plates of the frontals ; whereby these plates usurp in most mammals 
the office and the position of the external parts of the prefrontals in the cold- 
blooded vertebrata+. 
The posterior part of the coalesced prefrontals (figs. 24 & 25, 14) divides 
the anterior aperture of the cranium into two outlets, upon the inner cireum- 
ference of which the rhinencephala rest ; each outlet being commonly closed 
by part of the olfactory capsules, which are ossified and perforated to receive 
the divisions of the olfactory nerves. When the prefrontals extend backwards 
and beyond the cribriform plates, they form what is termed the ‘ crista galli’: 
this exists in comparatively few mammalia ; but is as large in the seal tribe 
as in man. In the tapirs the prefrontals expand above and overarch the ol- 
factory capsules, but their upper horizontal plates are overlapped by the 
nasals and true frontals. In the Delphinide, where the olfactory capsules 
are absent, the prefrontals expand posteriorly, and diverge from their median 
coalesced portions constituting the septum of the nasal passage, in order to 
form the posterior boundaries of those passages and the anterior wall of the 
cranial cavity. They again expand and form a thick irregular mass anterior 
to the nasal passages in some Delphinide, and in Ziphius ossification extends 
along the fibrous continuation of the prefrontals forwards to near the end of 
the premaxillaries{. They are connate with the orbitosphenoids behind, and 
soon coalesce with the vomer below; they rise anterior to the frontals and 
support the stunted nasals which are wedged between the prefrontals and 
frontals. The cetacea are the only mammalia in which the prefrontals appear 
upon the exterior of the skull, and which in this respect resemble the reptilia. 
* Lecons d’Anat. Comp. 1837, t. ii. p. 580. 
+ Cuvier takes this ground in objecting to Oken’s ethmoidal homology of the prefrontal 
in the crocodile, and says, “the ethmoid coexists in a cartilaginous state with, and is enve- 
loped by, the prefrontal, ‘comme la partie antérieure du frontal enveloppe l’ethmoide des 
ruminans.’”’—Hist. des Poissons, vy. p. 235. The correspondence is exaggerated, but it 
matters not. There are other characters of the mammalian ethmoid, as the closing of the 
cranium anteriorly, the transmitting the olfactory nerves, &c., which are nowise manifested 
by Cuvier’s cartilaginous ‘ethmoide’ in the crocodile, and are very satisfactorily so by the 
prefrontals in that animal. 
t Ossem. Foss. y. pt. i. p. 351. 
