420 Mr. Hunter’s Obfervations on the 
formed ; the natural elafticity of the parts themfelves, with 
the p refill re of the water oil the external fur face of the body, 
being greater than the refifiance of the air from within, will 
both tend to produce expiration without any immediate action 
of mufcles. 
The diaphragm, in thefe animals, appears to be the principal 
agent in infpiration ; and the cavity of the thorax not being in- 
tirely furrounded by bony parts, is of courfe lefs eafily expanded, 
and the apparatus for its expanfion in all directions, as in the 
quadruped, does not exift here. 
The Blow-hole , or Pajfage for the Air. 
As the nofe in every animal that breathes air is a common 
pafl’age for the air, and is alfo the organ of fmelling ; I (hall 
deferibe it in this tribe as infirumental to both thefe purpofes. 
There is a variety in feme fpecies of this animal which is, I 
believe, peculiar to this order ; that is, the want of the fen fe of 
lmelling; none of thofe which I have yet examined having 
that fenfe, except the two kinds of Whalebone Whale : fuch of 
courfe have neither the olfaClory nerves, nor the organ ; there- 
fore, in them, the nofirils are intended merely for refpiration ; 
but others have the organ placed in this paflage as in other 
animals. 
The membranous portion of the pofierior nofirils is one canal ; 
but when in the bony part, in mofi of them, it is divided 
into two ; the Spermaceti Whale, however, is an exception. 
In thofe which have it divided, it is in fome continued double 
through the anterior foft parts, opening by two orifices, as in 
the Piked Whale ; but in others, it unites again in the mem- 
branous part, making externally only one orifice, as in the 
7 Porpoife, 
