530 



the tympanic bone of the Baleena mysticetus and BaL ant- 

 arctica, since the condition of the fossils would not ad- 

 mit of the application of those differences in the deter- 

 mination of their affinities. 



Fig. 221. 



Tympanic bone of Balaena. qffinis, nat. size. Felixstow. 



One of the most complete of the fossil tympanic bones, 

 which measures five inches in length, resembles the BaL 

 antarctica in the slight elevation of the outer part of the 

 involuted convexity (a), and its gradual diminution to the 

 Eustachian end of the cavity (o) : it resembles both Baloena 

 in its traceable continuation to that end, and in the gradual 

 continuation of the concave outer wall (b) from the involuted 

 convexity ; this convexity is indented also, as in both 

 recent Balsense, by vertical fissures narrower than the mark- 

 ed indentation which distinguishes the BaL mysticetus : 

 these fissures are almost worn out by friction in some of 

 the specimens. The more perfect one under consideration 

 is not, however, identical with the BaL antarctica. 



The upper surface of the bone maintains a more equable 

 breadth from the posterior to the anterior end, the outer 

 angle of which, being well marked in the fossil, is rounded 

 off in the recent specimen ; the under and outer surfaces of 

 the tympanic bone meet at an acute angle. The above 



