Structure and Otconwny of Whales. 433 
others the union is by bony continuity, as in the Bottle-nole 
Whale, leaving a pafl'age on which the membrana tympani 
is ftretched, and another opening, which is the communica- 
tion with the linufes. 
The furface of the bone containing the immediate organ op- 
pofite to the mouth of the tympanum is very irregular, having a 
number of eminences and cavities. The cavity of the tym- 
panum is lined with a membrane, which alfo covers the fmall 
bones with their mufcles, and appears to have a thin cuticle. 
This membrane renders the bones, mufcles, tendons, &c. 
very obfeure, which are feen diftin&ly when that is removed. 
It appears to be a continuation of the periofteum, and the 
only uniting fubftance between the lmall bones. Befides 
the general lining, there is a plexus of veflels, which is 
thin and rather broad, and attached by one edge, the reft being 
loofe in the cavity of the tympanum, fomewhat like the plexus 
choroides in the ventricles of the brain. The cavity, we may 
fuppofe, intended to increafe found, probably by the vibration 
of the bone ; and from its particular formation we can eafily con- 
ceive, that the vibrations are conducted, or reflefted, towards 
the immediate organ, it being in fome degree a fubftitute for 
the external ear. 
The external opening being fmaller than in any animals of 
the fame fize, the membrana tympani is nearly in the fame 
proportion. In the Bottle-nofe Whale, the Grampus, and 
Porpoife, it is fmooth and concave externally, but of a parti- 
cular conftru&ion on the inner furface ; for a tendinous pro- 
cefs pafles from it towards the malleus, converging as it pro- 
ceeds from the membrane, and becoming thinner till its infertion 
into that bone. I could not difeover whether it had any mul- 
cular fibres which could affieft the a&ion of the malleus. In 
P p p 2 the 
