DEGLUTITION. 571 



to the distension of the nervous filaments, that surround the pectoral 

 portion of the canal. In the case of a female, labouring under a disease 

 which permitted the interior of the stomach to be seen, M. Halle noticed, 

 that whenever a portion of food passed into the stomach, a sort of ring 

 or bourrelet was formed at the cardiac orifice, owing to the mucous 

 membrane of the oesophagus being forced into the stomach by the con- 

 traction of its circular fibres. 1 The mucous fluid pressed out from the 

 different follicles, by the passage of the bolus, materially facilitates its 

 progress. 



Notwithstanding the facility with which deglutition is accomplished, 

 almost every part of it is uninfluenced by volition, being dependent 

 upon organization, and exerted instinctively. If the alimentary mat- 

 ter contained in the mouth be not sufficiently masticated ; or if it has 

 not the shape, consistence, and dimensions, it ought to possess; or 

 if the ordinary movements, that precede mastication, have not been 

 executed, whatever effort we may make, deglutition is impractica- 

 ble. We constantly meet with persons who are unable to swallow 

 the smallest pill ; and yet can swallow a much larger mass, if cer- 

 tain preliminary motions be executed, which, in the case of the pill, 

 are inadmissible, in consequence of its being usually of a nauseous 

 character. It appears, that the involuntary parts of the function are 

 excited by the stimulation of the aliment; for, if we attempt to swal- 

 low the saliva several times in succession, we find after a time, that 

 the act is impracticable, owing to the deficiency of saliva. Every 

 one must have experienced the difficulty of deglutition, when the 

 mouth and fauces were not duly moistened by their secretions. The 

 involuntary part of deglutition is under the control of the reflex system 

 of nerves. An impression is made by the alimentary matters upon the 

 excitor or afferent nerves, which impression is conveyed to the gray 

 matter of the spinal cord, and in the invertebrata to ganglia corre- 

 sponding to it; whence it is reflected to the muscular fibres that have 

 to be thrown into contraction. The portion of the spinal cord, which 

 serves as a centre for the reception of the impression, and the point of 

 departure for the motor influence, is the medulla oblongata; and the 

 experiments of Dr. John Reid 2 lead to the inference, that the glosso- 

 pharyngeal, which is chiefly distributed to the mucous surface of the 

 tongue and fauces, is the excitor nerve; the pharyngeal branches of the 

 pneumogastric, the motors. It would seem, however, that these nerves 

 do not alone possess the function ; for after they have been divided, the 

 animal is still capable of imperfect deglutition. The associate excitor 

 or afferent nerves, Dr. Reid concludes to be the branches of the fifth 

 pair, that are distributed to the fauces, and probably also those of the 

 superior laryngeal distributed to the pharynx : the associate motor or 

 efferent nerves being branches of the hypoglossal, that are distributed 

 to the muscles of the tongue, and to the sterno-hyoid, sterno-thyroid, 

 and thyro-hyoid muscles; filaments of the inferior laryngeal that ramify 

 on the larynx ; some of the branches of the fifth pair that supply the 

 levator muscles of the lower jaw; the branches of the portio dura that 



1 Op. cit., ii. 70. 2 ' Edinb. Med. and Surg. Journ., vol. xlix. 



