588 ANATOMY OF VERTEBRATES. 



there are no ' vocal cords/ but between them and the base of 

 the epiglottis are two lateral glandular fossae, representing the 

 6 ventricles ' : there are numerous orifices of mucous follicles along 

 the fore part of the base of the larynx. 



The external respiratory aperture, fig. 297,/, answering to the 

 nostrils of other Mammals, is single in all Cetacea, save the 

 Whales (Balcenidce), and is called the ' spout-' or ' blow-hole.' 

 Where it is single it is a transverse slit ; it is symmetrically situ- 

 ated, crescentic with the horns turned forward, in Delpliinidce ; 

 it is crescentic but oblique and to the left of the medial line in the 

 small Cachalot (Euphysetes) ; it is similarly unsymmetrical, but of 

 sigmoid shape in the great Cachalot (Physeter). The two nostrils in 

 the Whale-tribe are longitudinal. In all Cetacea the 6 spout-hole' 

 is at the upper surface of the head, readily emerging for inspira- 

 tion without unnecessary exposure of the animal. In the broad 

 truncate muzzle of the great Cachalot it is advanced to near the 

 anterior margin of that part : in other Cetacea it is mostly on the 

 same transverse parallel as the eyes. The direction of the nasal 

 passage is accordingly vertical: and as the lining or defining 

 membranes descend through the mass of adipose tissue to the 

 bony canal, the passage is dilated or produced into large irregu- 

 larly plicated sinuses or sacculi, ib. e, e. The first, toward the 

 fore part of the passage, is connected with the formation of the 

 anterior valvular prominence in Delphinidce, which fits into and 

 closes the outer crescentic aperture, at the will of the animal : 

 other muscles serve to open and dilate the spout-hole. The great 

 Cachalot, when gasping in the death-throes, opens it widely : in 

 the ordinary state it will admit, in the Whale, a man's arm. 

 Lower down, in the Porpoise, larger lateral narial sacculi extend 

 both forward and backward : the parietes of all these plicated ex- 

 pansions are invested by a layer of muscular fibres ; whereby the 

 water that may get access to them by the blow-hole, and to which 

 they serve as diverticula, can be expelled along with the expired 

 current of air. The number, size, and complexity of the narial 

 sacculi vary in different genera : Hunter remarks that ' the Sper- 

 maceti Whale has the least of this structure.' 1 In Delphinidce 

 the nasal meatus divides on entering the osseous part of the 

 passage, which is traversed by a medial prefrontal and vomerine 

 \ septum narium,'fig. 297, d: below this the passages again inter- 

 communicate and receive the swollen apex of the glottis. In the 

 small Cachalot {Euphysetes) the bony narial septum exists, but 

 the right meatus is so small that only the larger left one is tra- 



1 xciv. p. 371. 



