374 AN AMERICAN TEXT- HOOK OF PHYSIOLOGY. 



and Stuart and Mc< iormick ' have reported the case of a man in whom part 

 dt' the pharynx had been permanently removed by surgical operation and in 

 whom the epiglottis could he seen during the act of swallowing. In this 

 individual, according to their observations, the epiglottis was not folded back 

 during swallowing, but remained erect. hater observations by Kanthack and 

 Anderson, 2 made partly upon themselves and partly upon the lower animals, 

 (end, on the contrary, to support the older view. They state that in norma 1 

 ndividuals the movement of the epiglottis backward during swallowing m;i\ 

 be felt by simply passing the linger back into the pharynx until it conies into 

 contact with the epiglottis. At the beginning of the movement there is also a 

 contraction of the longitudinal muscles of the pharynx which tends to pull the 

 pharyngeal walls toward the bolus of food while, as has been said, the nearly 

 simultaneous contraction of the constrictors presses upon the food and forces 

 it downward. The food is thus brought quickly into the opening of the 

 oesophagus and the third stage commences. 



The transit of the food through the oesophagus is effected by the action 

 of its intrinsic musculature. The muscular coat is arranged in two layers, an 

 external longitudinal and an internal circular. These are composed of plain 

 muscle-tissue in the lower third or two-thirds of the oesophagus, but in most 

 mammals tiic upper third or more contains striated muscular tissue. The 

 chief factor in the transportation of the bolus through the oesophagus has 

 been supposed to consist in the contraction of the circular muscle. This con- 

 traction begins at the pharyngeal opening of the oesophagus and passes down- 

 ward in the form of a wave, peristaltic contraction, which moves rapidly in the 

 upper segment where the musculature is striated, and more slowly in the lower 

 segments in accordance with the physiological characteristics of plain muscle. 

 The result of this movement would naturally be to force the food onward to 

 the stomach. The longitudinal muscles of the oesophagus are without doubt 

 brought into action at the same time, but in this as in other cases of peristalsis 

 in tubular viscera it is not perfectly clear how they co-operate in producing 

 the onward movement. It may be that their contraction slightly precedes 

 that of the circular muscle, and thus tends to dilate the tube and to bring it 

 forward over the bolus. At the opening of the oesophagus into the stomach, 

 the cardiac orifice, the circular fibres of the oesophagus function as a sphincter 

 which is normally in a condition of tone, particularly when the stomach con- 

 tains food, and thus shuts off the cavity of the stomach from the oesophagus. - 

 In swallowing, however, the advancing peristaltic wave has sufficient force to 

 overcome the tonicity of the sphincter, or possibly there is at this moment a 

 reflex inhibition of the sphincter. In either case the result is that the food 

 is forced through the narrow opening into the stomach with sufficient energy 

 to give rise to a sound that may be heard by auscultation over this region. 3 

 According to measurements by Kronecker and Meltzer the entrance of the 



1 Journal of Anatomy mul Physiology, 1892. 



7 Journal of Physiology, I s '. 1 ."., vol. xiv. p. 154. 



3 See Meltzer: CentroJblatt fur die med. Wissenschaften, 1881, No. 1. 



