OCR Text |
Show 34 Mil. W. P. PYCRAFT ON THE [May 2, the mesethmoid by a horizontal plate of bone, almost rod-like in some species. The vertical, hamulate portion of the plate, by its upper limb, considerably adds to the width across the frontal, the lower, descending, process turns outwards to reach the quadrato-jugal bar. In the extraordinarily wide-mouthed genus Corydon, however, the quadrato-jugal bar stands far from this descending process. The olfactory chamber, owing to the extremely reduced condition of the maxillo-palatines, in the macerated skull is without a floor, in the majority of the genera of this group; but in two skullsjEurylcemus and Cymbirhynchus, in the British Museum Collection, this is more or less filled up by the ossification of a pair of turbinals, one on either side of the septum nasi, which apparently answer to the concha media. Pyriform in shape, each extends from the narial aperture backwards to the anterior horn of the vomer, where it becomes attached. Above and behind this is an oat-shaped and laterally compressed turbinal answering to the concha posterior. The nasal septum, in Calyptomena, is formed by a thin sheet of bone running along the whole length of the under surface of the nasal process of the premaxillfe. In Euryl&mus, Cymbirhynchus, and especially in Corydon, this septum becomes greatly swollen and grooved on its under surface. The Cranial Cavity.-The mesencephalic fossa is capacious. Its floor sweeps rapidly upwards to form a strongly marked basinshaped cavity. This upward rising of the floor is much more conspicuous than in some other genera, e. g. Menura or Corvus. The internal auditory meatus is represented only by a shallow depression. Immediately above and somewhat in front of this lies the trigeminal foramen. This, opening under a strong ridge, leads immediately into a deep groove across the floor of the mesencephalic fossa and thence through the under wall of the skull. All the branches of v leave by this foramen. There is no separate foramen for the ophthalmic (v1) (orbito-nasal); and in this respect the Eurylaemidfe appear to agree with all the other Passeriformes. The vagus foramen lies at the bottom of a deep fossa. The cerebellar fossa is small, relatively to the cerebral, sharply defined, and lias the supi'a-occipital region marked with prominent horizontal ridges. The floccular fossa forms a conspicuous moderately deep and more or less pyriform depression, sharply bounded caudad by the anterior semicircular canal. The mesencephalic fossa is of considerable size and, as in other Passeriformes, extremely well defined by a strong vertical ridge above, and an equally prominent ridge formed by the pro-otic below. The pituitary fossa takes the form of a narrow tube rising vertically from the floor of the skull. The dorsum sellce is reduced to a knife-like edge. The pre-pituitary region is produced into a moderately well-defined optic platform, triangular in shape. |