cd 
1369. ] CLASSIFICATION OF THE CARNIVORA. I, 
the surface of the already ossified petrosal, and forming no distinct 
prominence on the under surface of the skull*. Soon after birth this 
increases in 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. 
Fig. 6. 
5 
Section of the auditory bulla of the Tiger. 
oc. The outer chamber. 7c. The inner chamber. s. The septum. * The aper- 
ture of communication between the chambers. The other letters as in the 
preceding figures. 
The septum is formed by an inversion of the walls of both, applied 
together and ultimately perfectly fused in Fe/is, although, as will be 
seen, permanently distinct in some other allied formst. 
No indication of a carotid foramen can be seen anywhere on the 
* The cartilage from which the auditory bulla of the Felide is developed evi- 
dently corresponds with that lamella of the ‘‘ opisthotic” of Man which “ gra- 
dually 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 ‘ Ana- 
tomie du Chat’ (1845), vol.i. pp. 409 e¢ seg. He calls the outer chamber the 
‘“‘caisse du tympan, the inner one the ‘“‘cavité mastoidienne,’ 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 méme que quinze jours aprés la naissance ; et a six semaines il est en- 
tiérement formé, et a articulé avec tous les os voisins.” The septum, or “ cloison,” 
is “ commune aux deux os, formée par deux lames adossées et soudées entre elles.”’ 
Proc. Zoou. Soc.—1869, No. II. 
