ox THE TYMPANIC BULLA IN HYENAS. 303 



The Tympanic Bulla in Hycenas. 



Mr. R. I. PocoCK, F.R.S., F.Z.S., Curator of Mammals, gave 

 an exhibition, illustrated by lantern-slides, to show the pi'esence 

 of two chambers in the tym^Dauic bulla of the Hytenidse, and 

 remarked : — 



" In his paper upon the base of the skull in the Fissipede 

 Carnivora (P. Z. S. 1869, pp. 4-37), Prof. Flower laid stress 

 upon the presence or absence of a bony partition dividing the 

 cavity of the tympanic bulla into two compartments in the 

 ^^luroidea. Although on general grounds he followed Turner* 

 in classifying the Hysenas with the Felidae and Yivei-ridae, he 

 described the bulla of the Hysenas as ' perfectly simple within, 

 without trace of division into compartments' (p. 26). Subse- 

 quently, Mivart (P. Z. S. 1882, p. 199) wrote 'though there is 

 no septum, yet I have detected in both species oi'Hycena, inside 

 the auditory bulla, two osseous ridges or laminae, which, if 

 further developed, would divide off a small anterior chamber 

 from the much larger and externally more prominent posterior 

 portion.' These two papers appear to be the sources whence 

 subsequent authors, like Weber, Sedgwick, and others, have 

 derived their information ; Weber, following Mivart, described 

 the partition as low, and Sedgwick, following Flower, recorded it 

 as absent. 



Both Flower and Mivart were quite mistaken ; the bulla in all 

 Hypenas is divided by a strong partition into a larger outer or 

 anterior and a smaller inner or posterior chamber. 



It may be recalled that in the Felidfe and Viverridfe the 

 septum rises from the floor of the bulla and typically extends 

 upwards till it touches the periotic (petrous) bone. This par- 

 tition may arise just below the lower rim of the external auditory 

 meatus, or it may arise far away from that point. In the former 

 case the antero- external chamber is small, in the latter it is large 

 as compared with the postero-internal or posterior chamber ; but 

 the free edge of the partition always reaches, or is situated 

 close to, the same portion of the periotic, namely, the portion 

 which is pierced by the fenestra rotunda of the inner ear, and it 

 is always just at this point that there is a passage or orifice 

 between the two chambers. 



The outer chamber is itself partially divided from the external 

 auditory meatus by a horseshoe-shaped ridge or crest, the 

 tympanic ring, which is well shown in Flower's figure of the 

 section of the bulla of the Tiger (text-fig. 1, B, tr.). 



When the bulla of the inverted skull of the Hytena is opened 



* P. Z. S. 1848, pp. 63-88. Flower's paper is little more than an amplification of 

 this valuable paper by Turner, so far as the Carnivora are concerned. It does not 

 seem, however, that Turner was acquainted with this partition, his mention of the 

 division of the bulla into two parts referring to the superficial groove marking the 

 position of the partition. 



