ANATOM Y OK THE NAltWAL. 
141 
the blow-holes, now divided into two and form¬ 
ing distinct canals in the skull. They are closed 
by a valve b b (represented on an enlarged scale 
in the adjoining figure) resembling what is called 
a liare-lip, one lobe of which covers each canal. 
This valve, in the narwal, does not enter the ca¬ 
nal in the skull (as it does in the whale), hut 
merely closes flat down upon it; yet it effec¬ 
tually excludes the sea-water from the lungs, 
whatever he the pressure: it becomes, in fact, 
firmer and closer in proportion as the weight of 
water is greater. The valve is about six inches 
wide, and is opened and shut by two radiated 
muscles, c c. It is detached from the skull be¬ 
neath, about six inches from the pipes towards 
the snout. In consequence of this separation, 
the valve has sufficient freedom in itself, and 
sufficient room in the adjoining sac, to be drawn 
upward and forward, so as to expose the breath¬ 
ing canals; or falling upon them, like the valve 
or clapper of a pump-box, to secure them against 
the entrance of water. The two lobes of the 
valve are united together by a fleshy septum, 
connected slightly with the cartilaginous part of 
