AUDITORY BULLA IJN" THE MUSTELID^. 485 



d'. Tympanic ring projocting ass a strong semicircular ridge 



into cavity of bulla and attached to its roof by septa 



vvliicb, rat'ter-like, pass inwards and downwai'ds along 



roof and inner wall of the cavity. 



e. Cavity very incompletely divided by a median rafter 



arching high above the tympanic ring, leaving a wide 



space between its inferior edge and petrous portion 



of periotic Martes foina ; Charronia; Tayra. 



e'. Cavity much more completely divided by an additional 

 rafter, the inferior edge of which extends nearly hori- 

 zontally inwards and approaches much nearer the 



petrous portion of the periotic Martes martes ; Gulo ; Meles. 



a'. Cavity of bulla opening behind into a larger or smaller hollow 



space in external part of periotic. 



f. Cavity undivided, communicating with periotic hollow by 



means of a well-denned orifice opposite outer side of petrous 



portion of periotic (tympanic ring fused with roof of bulla). 



g. Walls of periotic hollow undifferentiated Conepatus. 



g'. Walls of periotic hollow with crescentic ridge and a passage 



reaching inwards io foramen laceriini posticum Mephitis, Spilogale. 



f'. Cavity more or less divided by rafter-like partition into an 

 anterior and a posterior chamber, the latter opening into 

 hollow of periotic. 



7i. Tympanic ring fused with roof of bulla ; a very narrow 

 space, nearly filled by the periotic between the two 

 chambers; the chambers much broken up by trabeculse . . . Qrisonella. 



h'. Tympanic ring projecting into bulla, the structure of which 

 closely resembles that described under heading d' . 



i. Periotic hollow smaller, only reaching to a point half- 

 way between paroccipital and tip of mastoid Mellivora. 



i'. Periotic hollow larger, extending to tip of hollow 

 mastoid. 



k. A bony septum separating posterior chambers of the 

 bulla from periotic hollow behind and leaving a 

 comparatively narrow passage of communication in 

 front ; inferior edge of partition betw^een chambers 

 of bullae evenlj' concave Ictonyx. 



Tc. Posterior chamber of bulla and periotic hollow 

 confluent throughout their extent ; inferior edge 

 of partition between chambers angularly arcuate 

 over petrous. 



I. Bulla abutting behind against nearly obsolete par- 

 occipital and confluent in front with hamular 

 process of pterygoid, as in Ictonyx Pcecilictis. 



I'. Bulla not reaching the stout, projecting parocci- 

 pital, and ceasing in front far behind hamular ... Taxidea. 



The three genera Poecilogale, Lyncodon, and Mydaus have heen 

 omitted from the table because from want of material my exami- 

 nation of the bullae was imperfect. So far, however, as the 

 available evidence goes they would fall provisionally as follows : — 

 Poecilogale under d alongside Lutra because the roof of the 

 bulla is thin and close to the tympanic ring, and its cavity is 

 undivided and not in communication with a hollow in the 

 periotic. The shape of the bulla is, however, very different from 

 that of Lutra. It is long, abuts against the paroccipital behind, 

 and has a short auditory tube as in Mustela. Its likeness to the 

 bulla of Lutra is no evidence of affinity between the two genera. 



