SECOND STAGE OF DEGLUTITION. 503 



fauces, into the mouth ; lower down, beyond the root of the tongue, is 

 the opening, e, into the larynx, I; at its termination, is that leading 

 into the oesophagus, 0. The walls of the pharynx consist chiefly of 

 three pairs of so-called constrictor muscles, supported by areolar tissue, 

 and lined throughout by a mucous membrane, continuous with that of 

 the nasal cavities, Eustachian tubes, mouth, larynx, and gullet. The 

 constrictor muscles, named, from their relative positions, superior, 

 middle, and inferior, overlap each other from below, that is, in the 

 opposite direction to the slates of a roof, the inferior muscle being 

 external to the middle one, and the middle one external to the upper 

 one ; the superior muscle, which is open in front, is, therefore, em- 

 braced, at its lower end, by the middle muscle, whilst this again is 

 embraced by the inferior constrictor. Considered together, these con- 

 strictor muscles are attached, above, to the base of the skull ; in front 

 and at the sides, to various parts of the bones of the skull and face, 

 and also to a fibrous band passing from the styloid process of the tem- 

 poral bone to the lower jaw ; still lower down, to the side of the tongue, 

 to the stylo-hyoid ligament, and the hyoid bone ; and, lastly, to the thy- 

 roid arid cricoid cartilages of the larynx. Posteriorly, the fibres of the 

 constrictor muscles, sweeping backwards in a curved direction, meet 

 at a raphe', or median line, along the back of the pharynx. Spreading 

 out on each side of the pharynx is the stylo-pharyngeus muscle, which 

 descends from the styloid process, and also the palato-pharyngeus, 

 which passes down in the posterior pillar of the fauces. The upper 

 portion of the pharynx, above the level of the soft palate, is exclusively 

 respiratory, and its mucous membrane is covered with a columnar cil- 

 iated epithelium ; the middle portion, through which not only air, but 

 food and drink pass, and the lower portion below the laryngeal aper- 

 ture, which is devoted exclusively to the passage of food and drink, are 

 covered with a squamous non-ciliated epithelium. Numerous simple 

 and compound racemose mucous glands open upon the pharyngeal 

 mucous membrane, and moisten it with their secretion. 



In the second stage of deglutition, the softened mass of food, forced, 

 by the backward movement of the tongue, into the middle portion 

 of the pharynx, is compressed, in rapid succession, from above down- 

 wards, by the lower fibres of the superior constrictors, and more espe- 

 cially by those of the middle and inferior constrictors, and thus is 

 propelled rapidly into the upper end of the gullet. At the same 

 time, the upper fibres of the superior constrictors, and especially the 

 fibres of the stylo-pharyngei muscles, draw upwards, and somewhat 

 outwards, the pharyngeal walls over the mass of food, as this is forced 

 downwards. The superposition of the constrictors, one upon the 

 other, from above downwards, facilitates the propulsion of the food in 

 that direction; moreover, the food itself meets with no obstruction 

 from. the edges of the two lower constrictors, as would have been the 

 case, had the imbrication of the muscles been in the opposite direc- 

 tion. The second stage of deglutition is rapidly performed, because 

 respiration is suspended during its occurrence. Provision must also 

 be made, during this stage of deglutition, for the safe transit of drink 

 and food through the pharynx into the gullet, without any drop or 



