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Show 1869.] CLASSIFICATION OF THE CARNIVORA. 17 the surface of the already ossified petrosal, and forming no distinct prominence on the under surface of the skull*. Soon after birth this increases iu size, and gradually assumes the bullate form of the wall of the inner chamber. In young animals, even some time after the ossification of the bulla is complete, the distinction between the two parts is clearly seen externally; not only are they marked off by a groove, but the tympanic portion has a more opaque appearance than the other. Section of the auditory bulla of the Tiger. o c. The outer chamber, i c. The inner chamber, s. The septum. * The aperture of communication between the chambers. The other letters as in tbe preceding figures. The septum is formed by an inversion of the walls of both, applied together and ultimately perfectly fused in Felis, although, as will be seen, permanently distinct in some other allied formsf. No indication of a carotid foramen can be seen anywhere on the * The cartilage from which the auditory bulla of the Felidce is developed evidently corresponds with that lamella of the "opisthotic" of M a n which "gradually wraps itself round the carotid, and so converts the primitive groove for the vessel into a complete tube, at the same time furnishing the inner part of its floor to the tympanum " (Huxley, Elements Comp. Anatomy (1864), p. 155). + These parts are all described in great detail in Straus-Durckheim's ' Anatomie du Chat' (1845), vol.i. pp. 409 et seq. H e calls the outer chamber the "caisse du tympan, the inner one the "cavite masto'idienne,' or "seconde chambre de la timbale," regarding it as the " analogue " of the mastoid cells of man This part, he says, " ne commence que par un seul point d'ossification qui ne parait m e m e que quinze jours apres la naissance ; et a six semaines il est entierement forme, et a articule avec tous les os voisins." The septum, or " cloison," is " commune aux deux os, formee par deux lames adossees et soudees entre elles." PROC. ZOOL. Soc-1869, No. II. |