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Show 286 }]]*. W. P. PYCRAFT ON THE [^pi'- 15, with an ossification of the basis of the choncha media which projects into the cavity from the outer wall. In the true Falcons the ossification of the aliethnioicl causes the anterior nares to be round in form as in life, in Polyboroides crescentic. In both, the aperture displays within its mouth a small median bony papilla- the papilla of the conclue veslibulum of Suschkin, the alinasal turbinal of W . K. Parker. The details of the structure of the cartilaginous nasal labyrinth and its ossifications have been exhaustively worked out and beautifully illustrated by Dr. Suschkin in his masterly monograph on the skull of Tinnunculus. The Cranial Cavity.-"Vhemetencephalicfossaol the Falconiformes is more basin-shaped in the smaller than in the larger forms. Moreover, in these smaller forms the anterior region of the fossa is tilted upwards and backwards so as to form an acute angle with the long axis of the skull. The trigeminal foramen, in Fcdco for instance, is sharply cut off from the mesencephalic fossa by an overhanging ledge of bone. The orbito-nasal foramen also lies immediately under this ledge. In the Vultures, the upper ledge of bone overshadowing these apertures is less extensive, so that they come to lie partly in the floor of the mesencephalic fossa. The apertures of the vagus and internal auditory meatus do not offer any very important points of difference for comment. The cerebellar fossa is sharply defined and variable in relative proportions, being, for instance, larger in Falco than in Vultur or Circus. The floccular fossa is, in Fcdco, cordiform, and apparently rather shallower than in other forms. The mesencephalic fossa is very sharply defined. It is banded above by a broad overhanging ledge formed by the tentorial ridge. The distinctness of its inferior border is blurred, in Vultur, by the apertures of the trigeminal and orbito-nasal nerves, which lie in the floor of the fossa. In Fcdco these are shut off from this fossa by a bony shelf, and open inward into the dorso-lateral border of the metencephalic fossa. The pituitary fossa is deep and tubular, and passes almost vertically downwards. The hinder boundary of this fossa, the dorsum sellce, forms a narrow ridge passing forwards and upwards to terminate above the oculo-motor foramen. The anterior border of the fossa is bounded by the transverse pre-pituitary ridge, which passes forwards into a narrow, sometimes triangular-, optic platform, on either side of which lie the optic foramina. The optic platform is continued upwards, forwards, and backwards into the pre-optic ridge which may be traced, in Circus for instance, on either side into the tentorial ridge. In the majority of other forms, probably, it disappears before reaching this, e. g. Vultur, Falco. The oculo-motor lies immediately caudad and ventrad of the optic foramen. It is continued backwards in a, rather wide groove into the dorsum sella?. Below and anterior to this foramen is the aperture for the internal ophthalmic artery-when this is separate. It opens into the pituitary fossa some distance from the |