1.38 



SKETCH OF THE HISTORY OF MAMMALIA. 



the skin, and the nostrils which conduct to them open 

 externally by a transverse semilunar slit, wliile very 

 strong muscular fibres, radiating from the entire circum- 

 ference of the ci-aniuni, cover the whole surface of the 

 apparatus, and act as compressors of the pouches. Let 

 us suppose, says Cuvier, " that the cetaceous animal 

 has taken into its mouth some water which it wishes to 

 eject ; it moves its tongue and jaws as if it were about to 

 swallow, but, closing the pharynx, it forces the water to 

 mount into the nasal passage, where its progress is ac- 



92. — Section of Head of Porpoise 



celerated by the action of the circular fibres, until it raises 

 the valves and distends the membranous pouches above. 

 Here it can be retained until the animal wishes to eject 

 it and take in breath. In order to spout, the valves being 

 closed, it forcibly compresses the pouches by means of 

 the muscular expansions which cover them ; and, com- 

 pelled to escape by the narrow crescentic aperture, it is 

 projected to a height corresponding to the force of the 



