THE MECHANISM OF SPOUTING. 409 



divided by a sort of slielf, is pi'olonged forwards, round, 

 and in front of, tlie anterior valve, and ends blindly in the 

 middle line above tbe anterior sac. The spiracnlar chamber 

 itself is produced, on each side, into a large lateral sac, the 

 walls of which are raised in strong parallel ridges, and 

 covered with a black papillose integument. The walls of 

 these sacs are strong and elastic. Layers of musciUar 

 fibres pass from the occipital ridge to the posterior lip of 

 the spii-acle, and from the edges of the maxillae to its an- 

 terior lip. Their action is necessarily to open the spiracle 

 and compress the sacs. There is no sphincter, the form of 

 the spiracle causing it to be naturally shut by the fitting to- 

 gether of its walls, and the pressure of the water upon them. 



When a Porpoise comes to the surface to "blow," the 

 shape of the posterior, concave, lip of the crescentic spiracle 

 does not sensibly alter; but the anterior, convex, lip is 

 pidled downwards and forwards, its surface becoming some- 

 what depressed, and its free edge nearly straight — so that 

 the aperture, when fully dilated, assumes the form of a 

 half -moon. At the same time, the air is expelled with a 

 rushing sound. The inspiratory act must be very rapid, as 

 the spiracle remains open for only a very short time after 

 expiration ends. When the larger Cetacea come up to 

 breathe, the expii-ed vapour suddenly condenses into a 

 cloud ; and, if expiration commences before the spiracle is 

 actually at the surface, a certain quantity of spray may be 

 di-iven np along with the violent current of the expelled 

 air. This gives rise to the appearance termed the " spout- 

 ing " of Whales, which does not arise, as it is commonly 

 said to do, from the straining off of the sea-water swal- 

 lowed with the food, and its expulsion by the nostrils. 



The epiglottis, in front, and the arytenoid cartilages be- 

 hind, are prolonged into a tapering tube, dilated at its sum- 

 mit 4nto a knob. The muscular soft palate embraces the 

 neck of this knob so closely that it cannot be withdrawn 

 without considerable effort. And thus, during life, the nasal 

 aii'-passages and the glottis are kept perfectly continuous ; 

 while the Porpoise dashes through the water, open mouthed. 



