ON THE AUDITORY BULLA IN TUG iM USTELID/E. 473 



24. The Auditory Bulla and other Cranial Characters in 

 the Mustelidffi. By R. I. Focock, F.R.S., F.Z.S. 



[Keceived March 22, 1921 : Kead May 10, 1921.J 

 (Text-figures 14-18.) 



Contents. 



Page 



Introduction 473 



The Foramina in the Base of the Skull 474 



The Internal Structure of the Auditory Bulla 478 



The Classification of the Genera hy the Bullag 484 



In 1869 (Proc. Zool. Soc. pp. 4-37) Flower described certain 

 features in the base of the skull of several genera of Mustelidse, 

 especially those connected with the auditory bulla and the 

 adjacent foramina, recording the position of the glenoid, carotid, 

 and condyloid foramina, and noting the shape and relative 

 prominence of the mastoid and paroccipital processes. In ma.ny 

 instances he opened the bullas find described the internal struc- 

 ture. The genera examined were Lutra, Enhydris, Meles, Taxidea, 

 Mephitis, Helictis, Arctonyx, Mydaus, Gulo, Mellivora, Gcdera, 

 Maries, Mustela, and lihabdogale \_=Ictoiiya;^. He summarised 

 the results of his examination of the skulls of the Ursidfe, Pro- 

 cyonidaj, and Mustelida^ as follows: — (1) The cavity of the bulla 

 is simple. . . . Tiiat is, although there are frequently trabeculae 

 or partial septa ]3iissing mostl}^ ti-ansversel}' across the lower part, 

 iiiid genei'ally connected with the tympanic ring, there is no 

 distinct and definite septum dividing it into a separate outer and 

 inner character [misprint for chamber]. (2) The paroccipital 

 process is more or less triangular, and directed backwards, out- 

 wards, and downwards, standing quite aloof from the bulla. This 

 relation depends cliiefly on the want of development of the 

 posterior portion of the bulla ; and is absent, or obscure, in 

 Mustela alone. (3) The alisphenoid canal is present in the 

 true Bears and Ailurus ; absent in all the others \i. e. in all 

 Mustelidae]. 



Although these statements have been copied over and over 

 again in works on the classification of the Carnivora, further 

 investigation shows that not one of them is exact. The bulla 

 of Helictis, for example, is as completely divided as in the 

 Felidfe, and there is a very distinct partition in Grison, Gido, 

 Mellivora, and other genera, although it is not so complete as in 

 the typical ^.-Eluroidea. As regards the paroccipital process, 

 although its prominence and remoteness from the bulla are well 

 marked in such geneiu as Lutra, Me2)hitis, Mellivora, Meles, 

 Taxidea, and others, it is in Helictis and Grison as closely 

 applied to the posterior end of the bulla as in typical Felidfe, and 

 it is even moi'e confluent with the bulla in Poecilictis than in 



