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Show 36 MR. GARROD ON THE NASAL BONES OF BIRDS. [Jail. 7, passes in front of the posterior terminations of the nasal processes of the prsemaxillse. But several birds present a very different condition. In Grus, for example, the posterior contour of the osseous external nares, instead of being rounded, as in holorhinal birds, is apparently formed by the divergence of two straight bars of bone, which enclose an angular space between them. These two processes evidently correspond to the two anteriorly directed cornua of the holorhinal skull described above; but they appear in many cases to be so different in density, and the outer one joins the body of the bone so abruptly, that it seems at first sight to be an independent ossification ; however, I have no reason to believe that such is the case. As in holorhinal birds, so in those under consideration, which may be termed schizorhinal, the internal process of the nasal bone runs forwards along the outer border of the nasal process of the prae-maxilla, and the outer descends free to join the maxilla. In these birds there is considerable variation in the manner in which the almost detached outer of the two nasal processes joins the body of the bone. In Numenius, Hcematopus, and many of the Limicolse they proceed directly upwards and expand, becoming slightly fanned out where they join the rest of the bone by a straight transverse line. In Ibis and Grus they are of uniform size from end to end, whilst in the Auks, and to a less degree in the Gulls, at its origin the process is slightly curved, being directed outwards for a short distance, and after that straight downwards and forwards. In most schizorhinal birds, a transverse line joining the extreme posterior point of one external nasal aperture to the similar one of the opposite side is situated behind the posterior ends of the nasal processes of the praemaxilla ; but in some of the short-beaked, broad-mouthed species of the class it is situated in front of them. Such is the case in Pterocles and Syrrhaptes ; and this peculiarity renders it at first sight uncertain whether they are schizorhinal at all; but as every intermediate condition may be found between the strictly schizorhinal skull of the Columbidse proper, and the very similar but less strongly marked skull of Pterocles, there is no real reason to doubt that the modification only depends on the great breadth of beak in the latter bird. The curious development of the superficial nasal turbinal bone of Pterocles is also a Columbine character, as is also the great length of the inner of the two nasal processes, which, in a manner quite unlike that of the Gallinae, extends on each side for a long way forwards under the premaxillary nasal splint. Subjoined is a list, alphabetically arranged, of the genera in which I have observed the schizorhinal arrangement:- SCHIZORHINAL BIRDS. Alca. Charadrius. Gallinago. Anous. Chionis. Glareola. Anthropoid es. Dromas. Grus. Arctica. Eurypyga. Hcematopus. Cataractes. Fratercula. Ibis. |
