OCR Text |
Show 9 MR. W. H. FLOWER ON THE [Jan.14, which is the original and first ossified ring-like portion of the tympanic bone. In the front of the floor of the bulla is the groove for the eustachian canal (e) ; between this and the anterior part of the tympanic ring, a low and thin ridge of bone with a concave free margin ises from the floor of the cavity. This is the only indication of any septum or division of the cavity of the bulla. Whether the whole of this bone is developed from the original tympanic, or whether the bullate inner portion is (as will be shown to be the case in some other Carnivora) ossified from a distinct cartilage of its own, I am not at present able to determine. In the youngest Bears' skulls that I have examined, the ossification of the whole bulla is continuous with that of the tympanic ring and floor of the meatus. Fig. 2. Section through the auditory bulla of Ursus ferox. Sq. Squamosal bone. T. Tympanic bone. BO. Basioccipital. g. Glenoid canal, a.m. External auditory meatus, t. Tympanic ring. e. Eustachian canal, car. Carotid canal. Behind the bulla (fig. 1, p. 7) the prominent and tuberous paroccipital process (p) projects downwards, outwards and backwards, standing quite off from the bulla, and only connected with it by a low laterally compressed ridge. Between the paroccipital process and the occipital condyle is a smooth concave surface, the front of which is excavated into a deep notch, the posterior boundary of the foramen lacerum posticum (1), between which and the condyle is the distinct subcircular foramen condyloideum (c), which transmits the hypoglossal nerve. At the outer side of the bulla, just behind the meatus auditorius externus, the mastoid process (m) is distinct and prominent, and widely separated from the paroccipital. At the bottom of a deep |