108 STUDIES IN TASMANIAN MAMMALS, LIVING AND EXTINCT, 



THE EXTERNAL EAR, AN OSTEOLOGICAL 

 COMPARISON. 



It is an interesting piece of parallel evolution to ob- 

 serve how closely the Nototherian ear simulates the condi- 

 tions obtaining among true Rhinoceroses, and then to' pass 

 in review the skull elements out of which they have been 

 developed. Although we have carried out this study 

 widely enough to embrace various Rhinoceroses, space for- 

 bids the publication of more than a small portion of our 

 data. 



In the Tichorhino Rhinoceros, the meatus auditorius 

 is formed by the post-glenoid — which is a powerful process 

 — reaching backwards to meet a similar contribution from 

 the mastoid, the line of junction being vertical ana cen- 

 tral. In a general way the Indian Rhinoceros repeats this 

 set of conditions, although the true ear bones may be 

 loose. If the photograph reproduced in plate xiii. is 

 appealed to, it will be seen that in Nototherium mitchelli 

 the loose tympanic tube of the Wombats is here strongly 

 inset, between the backward curve of the post-glenoid and 

 the forward sweep of the mastoid, the whole having 

 coalesced into a single element. 



Group departures from these conditions are found in 

 the Leptocerathine JVototheria, not sufficiently important to 

 detail here. ^ 3 ) Now let us see how these structural moie- 

 ties exist in the Wombats, and the Native Bear. 



Tasmanian Wombat. 

 There is a post-glenoid process, which is removed 

 mesiad from the contour line of the skull, and is shorter 

 than the mastoid process. The tympanic is tube-like, and 

 distinct, and the par-occipital is short. 



Hairy-Nosed Wombat. * 

 The post-glenoid is obsolete ; the mastoid is thin and 

 long; the tympanic is suspended mid-way between the 

 glenoid articular wall, and the mastoid amid deeply exca- 

 vated air cells. 



Native Bear. 

 Strong post-glenoid process (deeply excavated by air 

 cells), tympanic deeply set in a fossa between the post- 

 glenoid and the squamoso-mastoid process, long par- 

 occipital process. 



(3.) Briefly it may be said that the ear is a stage nearer the 

 primitive condition. 



