326 Mr. R. I. Pocock on the Auditory Bulla 
XXX VIII.—The Structure of the Auditory Bulla in existing 
Species of Felide. By R. I. Pocock, F.R.S., Super- 
intendent of the Zoological Society’s Gardens *. 
For distinguishing the genera and species of Felidz a great 
variety of cranial characters have been employed. One, 
however, seems to have escaped altogether the attention of 
systematists—namely, the size and position of the partition | 
dividing the tympanic bulla into two chambers. 
It may be recalled that the partition arises on the inner side 
of, and below, the tympanic annulus, and ascends towards the 
periotic bone, with which its free margin is in contact, or 
almost in contact, except posteriorly close to the fenestra 
rotunda. It thus cuts off the outer or auditory chamber of 
the bulla from the inner and posterior larger chamber 
except where the fenestra rotunda perforates the periotic, at 
which point there is a passage from the outer to the inner 
chamber. The posterior end of the partition is, to all intents 
and purposes, a fixed point, marked on the outside of the 
bulla by the stylomastoid foramen and on the inside usually 
by a ridge of bone formed by the indentation of the stylo- 
mastoid groove. But the position of the line of origin of 
the partition below the tympanic annulus and its anterior 
termination vary considerably in different species ; and the 
variations in these respects have a profound effect upon the 
relative sizes of the two chambers. When the partition 
rises close to the annulus and extends only slightly beyond 
the part of the periotic exposed within the bulla, the outer 
or auditory chamber is small and the inner chamber is large. 
Conversely, when it rises some distance below the annulus 
and passes forwards well in advance of the exposed portion 
of the periotic, the outer chamber is enlarged at the 
expense of the inner chamber. The line of the origin of 
the partition is generally marked on the outer surface 
of the bulla by a shallow groove, curving forwards from the 
stylomastoid foramen. 
I have recently pointed out + that the skull of the Snow 
Leopard or Ounce (Uncia uncia) differs very considerably 
from that of the Leopard (Panthera pardus), the Jaguar 
(P. onca), the Tiger (P. tigris) and the Lion (P. /eo), in the 
* The materials upon which the observations recorded in this paper 
are based are a series of skulls belonging to the Zoological Society, 
supplemented, mainly, so far as the external features of the bulla are 
concerned, by the skulls in the collection of the British Museum. 
+ Ann. & Mag. Nat. Hist. ser. 8, vol. xxxviii., Sept. 1916. 
— 
