486 ON THE AUDITORY BULLA IN THE MUSTELID.fi. 



It merely means, in my opinion, that they have inherited bullae 

 of a primitive kind, derivable fi'om the Martes-Tayra type, the 

 flattening in the two cases having been independently acquired. 

 Lyncoclon must be provisionally placed alongside Grisonella, and 

 Myclaus with Mephitis, Sjnlogcde, and Conepatus. 



Since such otherwise dissimilar genera as Meles and Galo or 

 Martes have similar bullae, it is probable that that type of bulla 

 is the most primitive in the Mustelidae. The rest of the bullaj 

 may be derived fronr it by modifications in different directions. 

 The flattening down of the roof on to the tympanic ring and the 

 shoi'tening of the posterior portion of the cavity gave rise to the 

 bulla of Lutra ; similar flattening of the roof and the development 

 of a complete oblique partition to that of Helictis ; thickening of 

 the walls with spongy bone filling the spaces between the main 

 sejDta to that of Mustela • and the openiug of the posterior 

 chamber into the hollow of the periotic to that of Mellivora. 

 From the latter may be derived the bullae of Ictonyx, Poecilictis, 

 and Taxidea by extension of the periotic space, and in the case of 

 Grisonella t\\\s was accompanied by the flattening of the bulla and 

 the confluence of its roof with the tympanic ring and reduction 

 of the posterior chamber. The bulla of Mephitis and other 

 Skunks may also be derived from the type seen in Mellivora by 

 the disappearance of the partition behind the petrous portion of 

 the periotic, shortening of the portion of the cavity behind it, 

 and the forward movement of the orifice by which the cavity 

 communicates with the greatly enlarged periotic hollow. 



