in DIGESTION IN THE MOUTH AND STOMACH 163 



alone is heard, exhibit atony of the cardia, since during coughing 

 regurgitatiou of food from the stomach into the oesophagus readily 

 occurs ; in those, on the contrary, in whom the cardia is normally 

 closed, which prevents the bolus from entering the stomach imme- 

 diately, it remains at the lowest part of the oesophagus, until the 

 contractile movement of the latter overcomes the resistance of the 

 cardia, and produces the terminal murmur, which, as seen above, 

 occurs 6'7 seconds after the commencement of deglutition. 



The human cardia is thus normally closed, so that the bolus 

 (or fluid mass) must remain at the extreme end of the oesophagus, 

 until the contractile movement of the latter forces it into the 

 stomach. This closure of the cardia explains why the increment 

 of pressure determined by Krouecker and Falk in the gullet 

 during deglutition, does not occur within the stomach. 



Kronecker, therefore, differs from Magendie, in not admitting 

 three successive stages in the act of swallowing. He maintains 



O t O 



that deglutition occurs in one single act in which the bolus (liquid 

 or pulp) is shot with great velocity and under a relatively high 

 pressure, as far as the cardia. This, he says, is the fundamental 

 mechanism of deglutition, in which neither the muscles of the 

 pharynx nor those of the oesophagus participate, the bolus being 

 allowed to slide through passively. The whole canal contracts in 

 successive sections only when the bolus has already reached the 

 cardia, and this accessory movement is an act complementary to 

 the normal act of swallowing, which may acquire vital importance 

 in cases in which a bolus too large or too hard is being swallowed, 

 and sticks in the oesophagus owing to the insufficient impulse, 

 producing painful sensations of choking, which have to be removed 

 by repeated acts of swallowing and drinking of fluid. 



The principal factor in the normal act of deglutition is repre- 

 sented by the muscles of the mylohyoid group, as already recognised 

 by Magendie, Tourtual, Ludwig. Of this we have direct evidence 

 iu the fact that on dividing the mylohyoid fibres of the motor 

 branch of the fifth nerve, while the filaments that supply the 

 digastric muscles are left intact, the animal is no longer able to 

 swallow, unless it resorts to the expedient of throwing its head 

 back quickly with the mouth open, so as to jerk the food into the 

 throat, when the pharyngeal constrictors can come into play 

 effectively. The muscles innervated by the hypoglossal are also 

 important to the act of deglutition, which is disturbed by their 

 resection, owing to the consequent paralysis of the longitudinal 

 lingual muscle and of the hypoglossal. By the almost simultaneous 

 contraction of this group of muscles (with which is associated that 

 of the group of elevator muscles of the hyoid bone and larynx), the 

 bolus conveyed to the back of the tongue is pressed between tongue 

 and palate, and driven under strong pressure towards the point of 

 least resistance, i.e. towards the retro-buccal cavity, while the 



