| OCR Text |
Show 386 MR. W. P. PVCRAFT ON THE [Mar. 21, bone from the dorsal region of the rim of the optic foramen forwards to the interorbital plate. The orbitosphenoid in the Diomedeidae is completely ossified ; the roof of the orbit is more or less perfectly protected by a supra-orbital ledge, such as occurs in the Penguins. The optic foramina in Diomedeidas, Ossifraga, Fulmarus, Priocella, Prion, Daption, Thalassceca, and some species of Puffinus and CEstrelata, are divided by a median septum one from another; in the rest the septum is absent and the two apertures are confluent. The ethmoidal region.-The mesethmoid is indistinguishably fused below with the parasphenoidal rostrum, from Avhich it rises as a thin vertical plate of bone, in the median line. Its dorsal border is expanded so as to underlie the nasal and frontal bones, extending outwards on either side to the level of the free edge of the supraorbital groove. The anterior border of the mesethmoid is of considerable width; postero-dorsally it extends backAvards to play the part of a crista-galli dividing the olfactory fossce into right and left lateral chambers ; its postero-ventral border is merged with the interorbital septum when present. The aliethmoid is only the ectoethmoidal ossification and forms the antorbital plate. This, in the Procellariidas, is generally of very considerable size. In Bulweria it takes the form of an almost vertical plate of bone, projecting nearly at right angles from the posterior border of tbe mesethmoid, and running outwards to the lachrymal. Its dorsal border becomes continuous with the free edge of the expanded mesethmoid. Its postero-dorsal angle is more or less hollowed out and trends downwards to join the median horizontal bar of bone representing the interorbital septum. This antorbital plate serves to enclose tAvo spacious olfactory chambers divided one from another by the mesethmoid. Anteriorly they are in direct communication with the lachrymo-nasal fossa, posteriorly AAith the brain-cavity. Procellaria, Oceanites, and Cymodroma more or less resemble Bulweria in this respect. In Fulmarus, Thalassceca, CEstrelata, Daption, and Prion the form of the antorbital plate resembles that just described. In these genera, however, the outer border is fused with the lachrymal. In all the genera so far enumerated the dorsal border of the lachymal is pierced by two foramina. Of these, one lies immediately under the free edge of the frontal, and the other between the lachrymal and the aliethmoidal wall. In Priocella these two foramina are merged into one, forming a deep emargination between the dorsal Avail of the antorbital plate and the frontal; externally this plate and the lachrymal are fused as in Fulmarus, &c. The outer of these tAvo foramina-the lachrymal-in Priofinus, Majaqueus, and Puffinus is of great size ; in all except a few species of Puffinus the antorbital plate remains distinct from the lachrymal. In the Diomedeidas the antorbital plates are represented by a pair of narrow lateral Avings, Avhich never extend dorsally to meet the frontal. In Phcebetria they extend laterally so as to pass behind, and project slightly beyond, the level of {he lachrymal. |
