480 Mil. R. I. POCOCK ON THE 



the bulla, is almost in contact with the superjacent portion of the 

 roof, to Avhich it is attached by two or three very shallow rafters. 

 The posterior rafter, present in Meles, Gido, and Maries martes, 

 is undeveloped, the only trace of subdivision of the cavity being- 

 supplied by a rafter which extends transversely from the ring 

 along the roof and inner wall of the bulla to a point just behind 

 the orifice of the carotid canal; and, as indicated on the outside 

 of the skull, the cavity of the bulla posteriorly is far in advance 

 of the paroccipital process. Except for its flatness the bulla is 

 very like tliat of Tayra or Martes foina. 



In Poecilogale, judging from a skull with a partially fractured 

 bulla in the British Museum, it seems that the walls of the bulla 

 are thin, not spongy, and that the cavity, reaching posteriorly to 

 the paroccipital, is simple and undivided except by incomplete 

 raftei-s, and does not communicate with a chamber hollowed out 

 in the mastoid, which is quite small. This genus therefore has 

 a simpler, more primitive bulla than is seen in Mustela or in 

 Ictonyx. 



Another type of bulla is found in Gale nivalis, africana, Mustela 

 erminea, hihernica, and Putorius putorius and furo. The cavity 

 of the bulla is continuous from end to end, being undivided by 

 septa ; but it is greatly reduced in size by the thickness ©f its 

 walls, which, instead of being composed of solid bone, thicker or 

 thinner, as the case may be, in the genera previously described, 

 is composed of spongy bone permeated with air-cells. These fill 

 the entii'e space above the tympanic I'ing, and almost obliterate 

 the portion of the cavity behind the j^etrous portion of the 

 periotic and also the anterior part of the cavity. There is no 

 definite hollow space in the external portion of the periotic ; but 

 this bone is spongy and porous like the walls of the bulla itself, 

 and its spaces communicate with the cavity of the bulla. 



The bulla of Helictis {H. everettii) is quite unique. The tympanic 

 ring is fused to the roof but not to the same extent as in 

 GrisoneUa and Mephitis, its free edge projecting slightly, even in 

 the middle of its curve, and more so in front and behind. The 

 anterior rafter resembles that of GrisoneUa ; bvit the posterior 

 rafter, rising low down on the tympanic ring behind, runs 

 obliquely forwards and inwards to terminate on the floor of the 

 bulla just inside the point where the orifice of the carotid canal 

 opens. Its inferior edge is closely clamped on to the petrous 

 portion of the periotic except at one point situated externally 

 towards the stylomastoid, where thei-e is a notch in the partition 

 rafter close to the Je7iest7'a rotunda. Thus the bulla is completely 

 divided into two subequal chambers, except where the notch in 

 question affords a passage between them — a precisely similar 

 formation to that which is well-known in many ^luroidea. The 

 posterior chamber has a few low marginal ridges on its inner and 

 posterior walls, and the anterior end of the anterior chambei' has 

 a few ridges in addition to the anterior rafter. The external 

 portion of the periotic is not hollowed. 



