May, 1890.] 



ELLIOTT SOCIETY. 



«39 



scribed somewhere, but by whom, and in what particular animal I cannot re- 

 call". 



"With these doubts as to the existence of a description already inprint, I 

 have concluded to prepare this account of what I have observed for this Jour- 

 nal, notwithstanding the possibility of another being eventually discovered. 



I \n\l add that I have submitted the bone to Dr. Middleton Michel, of the 

 Medical College of South Carolina, and that he believes ' ' it to be a relic of 

 embryonal development, representing the tympanic bone, which has only par- 

 tially coalesced with the petrosal, still retaining its ring-like appearance". 



A moment's examination of the Chinchilla skull shows an enormous develop- 

 ment of the cavities connected with the mechanism of hearing, thus intensify- 

 ing the sound which enters said cavities. In addition to this the external ear is 

 unusually large — more so in fact than in probably any other animal of the 

 same size now living. With these two conditions the sense of hearing in the 

 Chinchilla must be necessarily very acute. 



Skull of Chinchilla lanigera, with view of bone attached 

 to ear twice its natural size. 



With regard to its purpose, my opinion is that it is not an ossification of the 

 cartilaginous meatus intemus, as that is a part of the petrosal, which is soft in 

 early life and becomes joined to it later by ossification, whereas this bone is en- 

 tirely separate and distinct. Its size is such that it should not escape the no- 

 tice of a careful dissector, and it is an important detail of the skull whether 

 seen from above or from the side. It doubtless exists in other rodents, although 

 perhaps never so large in proportion to the head as in Chinch ilia. Its purpose 

 would appear to be for the more secure attachment of the large external ear, 

 which a dissection of the adjacent soft parts will most likely prove to be true. 



