24 



SPECIMENS OF CETACEA. 



8. Tympanic bone, right; length 5^ inches, 3 inches in 



greatest breadth and 4-|- inches in vertical height. 

 The outer surface presents two convex divisions, 

 separated by a long, wide, deep groove ; the posterior, 

 much the larger, has on it a shallow groove which 

 limits the lip-like process behind; lower down the outer 

 surface is concave. The inner surface is convex, and 

 striated with vertical grooves. The lower aspect 

 presents a strong keel-like ridge which extends along 

 its whole length. At the upper, moderately thick, 

 horizontal border of the inner surface the tympanic 

 cavity opens, the anterior or Eustachian end being 

 slightly notched. Knox Collection. 



9. Tympanic bone, right. Nos. 9, 10, 11 similar to No. 8 in 



their characters. Knox Collection. 



10. Tympanic bone, right. 

 September 1888. 



Donor — Mr John M'Donald, 

 s.s. " Maud," Dundee. 

 Turner Collection. 



11. Tympanic bone, right. 



12. Tympano-periotic bones. 



Tympanic 6 inches 



adult, left, fused 

 lonof, 31 inches 



together, 

 in o-reatest 



breadth ; height 4J inches ; surfaces and keel-like 

 ridge strongly marked ; lip-like process bounded 



