420 ORGAN'S OF THE SENSES. 



tween these two cavities. Many suggestions have been made 

 as to the probable use of this tube : some have supposed that 

 it is intended to enable us to hear our own voice ; the bones 

 of the head, however, serve to propagate this sound, and 

 besides, in its normal condition, the tube is closed ; if, by any 

 cause, it is opened for any length of time, the person hears, 

 not only his own voice, but every sound produced in the 

 upper part of the body, such as the sound of the breathing, 

 the movements of the velum of the palate, of the tongue, 

 etc.; it has been observed, in some <jases of this kind, that 

 patients whose attention was thus constantly directed to the 

 various phenomena of the organism have at length become 

 hypochondriacs, an effect which is generally produced by 

 paying too much attention to the facts of our own internal 

 organic existence (see p. 56). 



The Eustachian tube is then normally closed by means of 

 the juxtaposition of its walls, and opens only when some 

 special organ separates these, by acting on the membran- 

 ous and movable outer wall, and drawing it away from 

 the other, which is cartilaginous and quite stationary. This 

 office is performed by the circumflexus or tensor palati, or 

 muscle of the velum of the palate, and the effect of the 

 opening thus made is to bring the air of the drum into com- 

 munication with that of the nasal chambers, that is to say, 

 the external air. The muscles of the velum of the palate, 

 however, contract only during the movements of deglutition ; 

 the act of swallowing cannot take place when there is 

 nothing to swallow, and requires, at least, a few drops of 

 saliva. We return, therefore, to what we have already said 

 on the subject of salivation and deglutition, when we pointed 

 out that the first of these functions is closely connected 

 with the normal operation of the sense of hearing ; and also 

 observed that the secretion of the saliva, which is almost 

 useless in the carnivorous animals, as regards digestion, is 

 chiefly connected with the intermittent movements of de- 

 glutition, which may be compared to the winking of the eyes 

 and are intended to effect the opening of the Eustachian 

 tube (see pp. 222 and 226). This is why we make similar 

 movements of deglutition, even when asleep, and especially 

 in ascending great heights, because, beside the variations in 

 the exterior air which render a restoration of equilibrium 

 necessary, the gaseous exchanges of the blood have the 

 effect of varying the tension of the interior air ; these ex- 

 changes are sometimes very sudden and of considerable 



