342 PHILOSOPHICAL TRANSACTIONS. [aNNO 1787. 



the external opening having a particular form would incline us to believe that 

 something was conveyed to the tympanum. 



The bony part of the organ is very hard and brittle, rendering it even difficult 

 to be cut with a saw, without its chipping into pieces. That part which con- 

 tains the immediate organ is by much the hardest, and has a very small portion 

 of animal substance in it; for when steeped in an acid, what remains is very soft, 

 almost like a jelly, and laminated. The bone is not only harder in its substance, 

 but there is on the whole more solid bone than in the corresponding parts of 

 quadrupeds, it being thick and massy. The part containing the tympanum is a 

 thin bone, coiled on itself, attached by one end to the portion which contains 

 the organ; and this attachment in some is by close contact only, as in the nar- 

 whale; in others the bones run into one another, as in the bottle-nose and piked 

 whales. The concave side of the tympanum is turned towards the organ, its 2 

 edges being close to it; the outer is irregular, and in many only in contact, as 

 in the porpoise; while in others the union is by bony continuity, as in the 

 bottle-nose whale, leaving a passage on which the membrana tympani is stret- 

 ched, and another opening which is the communication with the sinuses. 



The surface of the bone containing the immediate organ opposite to the 

 mouth of the tympanum is very irregular, having a number of eminences and 

 cavities. The cavity of the tympanum is lined with a membrane, which also 

 covers the small bones with their muscles, and appears to have a thin cuticle. 

 This membrane renders the bones, muscles, tendons, &c. very obscure, which 

 are seen distinctly when that is removed. It appears to be a continuation of the 

 periosteum, and the only uniting substance between the small bones. Besides 

 the general lining, there is a plexus of vessels, which is thin and rather broad, and 

 attached by one edge, the rest being loose in the cavity of the tympanum, some- 

 what like the plexus choroides in the ventricles of the brain. The cavity we may 

 suppose intended to increase sound, probably by the vibration of the bone; and 

 from its particular formation we can easily conceive that the vibrations are con- 

 ducted, or reflected, towards the immediate organ, it being in some degree a 

 substitute for the external ear. 



The external opening being smaller than in any animals of the same size, the 

 membrana tympani is nearly in the same proportion. In the bottle-nose whale, 

 the grampus, and porpoise, it is smooth and concave externally, but of a par- 

 ticular construction on the inner surface; for a tendinous process passes from it 

 towards the malleus, converging as it proceeds from the membrane, and be- 

 coming thinner till its insertion into that bone. I could not discover whether it 

 had any muscular fibres which could affect the action of the malleus. In the 

 piked whale, the termination of the external opening, instead of being smooth 

 and concave, is projecting, and returns back into the meatus for above an inch in 



