4ii Mr, Hunter's Obfervcums an the 
openings form a paffage for the air in refpiration to and from 
the lungs ; for it would be impoffible for thefe animals to 
breathe air through the mouth; indeed, I believe, the human 
fpecies alone breathe by the mouth, and in them it is moftly 
from habit ; for in quadrupeds the epiglottis condufrs the 
air into the nofe. 
In the whole of this tribe, the fituation of the opening on 
the upper furface of the head is well adapted for this purpofe, 
being the firft part that comes to the furface of the water in 
the natural progreffive motion of the animal ; therefore it is to 
be confidered principally as a refpiratory organ, and where it 
contains the organ of fmell, that is only fecondary. 
As the animals of this order do not live in the medium which 
they infpire, the organs conducing the air to the lungs are in 
fome fort particularly conftru&ed, that the water in which 
they live may not interfere with the air they breathe. 
The projecting glottis, which has been defcribed, paftes into 
the pofterior noftrils, by which means it erodes the fauces, di- 
viding them into two paftages. Th^ enlargement at the termi- 
nation of the glottis, obfervcd in fome of them, would feem 
to be intended to prevent its retraction ; but, as it feems con- 
fined to the Porpoife and Grampus, it may, perhaps, in them 
anfwer fome other purpofe. 
The beginning of the pofterior noftrils, which anfwers to the 
palatum molle in the quadruped, having a fphin&er, the glot- 
tis is grafped by it, which renders its fituation ftill more fecure, 
and the paffages through the head,acrofs the fauces and along the 
trachea, are rendered one continued canal; this union of glottis 
and epiglottis with the pofterior noftril, making only a kind of 
joint, admits cf motion, and of dilatation and contraClion of the 
fauces, in deglutition, from the epiglottis moving more in or 
out of the pofterior noftril. 
This 
