306 MR. R. I. POCOCK ON THE 



cavity continuous with the eustachian tvibe and the external 

 auditoiy meatus. This cleft deeply notches the floor of the large 

 cavity, and the floor slopes backwards and upwards from the 

 cleft, through which a portion of the periotic is visible, to the par- 

 occipital process. The edges of the cleft are no doubt the ' two 

 osseous ridges or laminpe which, if further developed, would 

 divide off a small anterior chamber from the much larger .... 

 posterior portion,' described by Mivart. That is true ; but the 

 two chambers would not cori'espond to the two present in the 

 Tiger, for the outer of the two laminse is the tympanic ring, and 

 is therefore not the homologue of the partition dividing the 

 Tiger's bulla, as Mivart supposed. The ' small anterior chamber ' 

 of the bulla, which is exceptionally large in the Hyaenas, is 

 merely the anterior part of the tympanic chamber. 



Whether Flower correctly interpreted this lamina as the 

 tympanic ring or not, does not appear ; but he may be given the 

 benefit of the doubt. Nevertheless, both he and Mivart failed 

 to detect that where the apparent floor — or roof, if the skull be 

 held in its normal position^of the bulla abuts against the 

 periotic, there is quite a distinct orifice through which a probe 

 can be passed backwards into a second chamber lying behind and 

 below the apparent floor of the bulla. This chamber can be laid 

 open by cutting away the paroccipital bone externally to the 

 occipital condyle. It will then be seen quite clearly that the 

 bony plate, regarded by Flower and Mivart as the floor (or roof) 

 of the bulla, is, in reality, a partition dividing the bulla into two 

 chambers, and passing from the periphery of the cavity of the 

 bulla to the periotic, exactly as is the case in the Tiger, allowance 

 being made for the origin of the partition much farther back 

 thanin that Feline. It is not, however, much farther back than 

 in some other ^luroids, e. g., Cynictis. 



Nevertheless, it is not certain, in my opinion, that the par- 

 tition in the Hysenas is the exact homologue of that of the Cats. 

 The inner wall of the posterior chamber of the bulla in -^luroidea 

 is often strengthened by bony crests or ridges of varying height, 

 and one such crest, curving round the back of the chamber and 

 occupying the position of the partition, where it rises from the 

 bulla near the paroccipital, in Hyaena, is present in two immature 

 skulls of Proteles, in addition to the normal vertical partition 

 which in these specimens is thin and imperfectly ossified or fene- 

 strated. The interest of this fact lies in the circumstance that 

 Proteles in several of its cranial characters occupies a position 

 midway between Hycnia and the Mungotinse. Hence it is possible 

 that in Hycena the normal partition has been replaced by a 

 secondary partition of stronger, growth. However that may be, 

 it is quite clear that the bulla of HycBna can no longer be 

 described as undivided. 



Two other points of systematic importance may be alluded to : 

 the bulla in Hysenas is fused anteriorly to the basisphenoid, as 



