Structure and Oeconomy of Whales. 419 
the pofterior mediaftinum. The lungs are extremely elaftic in 
their fubftance, even fo much fo as to fqueeze out any air that 
may be thrown into them, and to become almoft at once a 
folid mafs, having a good deal the appearance, confidence, and 
feel of an ox’s fpleen. The branches of the bronchia? which 
ramify into the lungs have not the cartilages flat, but rather 
rounded ; a conftru&ion which admits of greater motion be- 
tween each. 
The pulmonary cells are fmaller than in quadrupeds, which 
may make lefs air neceflary, and they communicate with each 
other, which thofe of the quadruped do not ; for by blowing 
into one branch of the trachea, not only the part to which it 
immediately goes, but the whole lungs are filled. 
As the ribs in this tribe do not completely make the cavity 
of the thorax, the diaphragm has not the fame attachments as 
in the quadruped, but is connected forwards to the abdominal 
mufcles, which are very ftrong, being a mixture of mufcular 
and tendinous fibres. 
The pofition of the diaphragm is lefs tranfverfe than in the 
quadruped, paffing more obliquely backwards, and coming very 
low on the fpine, and higher up before ; which makes the cheft 
longeft in the direction of the animal at the back, and gives 
room for the lungs to be continued along the fpine. 
The parts immediately concerned in infpiration are extremely 
ftrong ; the diaphragm remarkably fo. The reafon of this 
muft at once appear; it neceflarily requiring great force to ex- 
pand in a denfe medium like water, efpecially too when the 
vacuity is to be filled with one which is rarer, and is to water a 
fpecies of vacuum, the preifure being much greater on the 
external furface than the counter-preffure from within. But 
expiration on the other hand muft be much more eafily per- 
formed ; 
