226 report— 1846. 



in birds. " 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 

 la paroi anterieur de 1'orbite, a l'endroit ou le frontal anterieure se trouve 

 ordinairement, est manifesteraent formee 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 vertebrataf . 



The posterior part of the coalesced prefrontals (figs. 24 & 25, 14) divides 

 the anterior aperture of the cranium into two outlets, upon the inner circum- 

 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 DeJphinidcB, 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 Defphinidce, 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. 



* Leeous d'Anat. Comp. 1837, t. ii. p. 580. 



f 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, ' com me la partie anterieure du frontal enveloppe l'ethmo'ide des 

 ruminans.' " — Hist, des Poissons, v. p. 235. The correspondence is exaggerated, but it 

 matters not. There are other characters of the mammahan 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. 



J Ossem. Foss. v, pt. i. p. 351. 



