478 MR. R, I. POCOCK ON THE 



the glenoid foramen and some distance from the foramen lacerum 

 posticum. Its position varies in accordance with the inflation of 

 the bulla, and every gradation can be traced from Mustela, where 

 it is thrust far out, to Gulo, Lutra, and Mephitis, where it lies far 

 in towards the foramen lacerum posticum. It is relatively closer 

 to the latter orifice in the Skunks than in other genera. 



The Internal Structwe of the Aiulitory Bulla. 



The bulla of Meles meles may be described as representing a 

 common type in the family*. 



The tympanic ring projects far into the cavity of the bulla as a 

 large semicircular lamina. The space between it and the roof of 

 the bulla is divided into chambers by a few vei-tical, arched, bony 

 plates, arising from the lamina and the superjacent roof and 

 extending transversely inwaixls on to the inner wall. These may 

 be called the rafters. There is also a tolerably large plate rising 

 from the upper side of the tympanic ring in front and extending 

 horizontally forwards to the bottom of the anterior wall of the 

 bulla, terminating internally at a point where the bulla touches 

 the foramen lace7^2{.m viedium. Behind this point the floor of the 

 cavity is subdivided by low anastomosing ridges into a number of 

 pockets. 



■ The posterior portion of the tympanic ring lies just above the 

 fenestra rotunda on the periotic bone ; and the posterior rafter, 

 rising about one-fourth of the distance from the posterior end of 

 the tympanic ring, arches high above the periotic, and terminates 

 about half-way down the inner wall of the cavity. This rafter, 

 supplemented hy the posterior end of the tjanpanic ring, partially 

 divides the cavity of the bulla into an anterior larger and a 

 posterior smaller chamber. Nevertheless there is a wide passage 

 between them above the periotic bone. The posterior part of the 

 cavity of the bulla is closed behind, and does not extend beyond 

 the limits of the bulla as defined externally. 



The bulla of Martes martes resembles that of Meles in all 

 essential respects, the posterior i-after being well developed ; but 

 in M.foina all the rafters are less well develoiDcd, the posterior 

 being quite short. 



In Charronia flavigula there is only a single rafter arising 

 from about the middle of the tympanic ring, arching with a 

 strong concave curve to the roof, then descending to the floor 

 along the inner wall of the bulla. 



Tayra harhara resembles Charronia except that the rafter is 

 less elevated and less arcuate. 



Gulo gulo is very like Meles and Martes martes, but the pos- 

 terior rafter has the lower edge, not lightly concave as in those 



* In this paper the bulla is described as seen when the skull is inverted. Hence 

 the periotic forms part of the floor of its cavity ; and the cavity is bounded by the 

 roof above and by the anterior, inner, and posterior walls. Flower described it as 

 seen when the skull is in its natural position, and I followed that course in the case 

 of the Felidse (Ann. Mag. Nat. Hist. (8) xviii. pp. 326-334, 1916). 



