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ANATOMY AND PHYSIOLOGY OP 



" Stmcture. — The pharynx is in part 

 muscular, and in part membranous. Of 

 the muscles belonging to it Ihe constric- 

 tors are those that more immediately enter 

 into its composition. They are so dis- 

 posed as to give the membrane forming 

 the sac a complete fleshy covering, which 

 is rendered the more uniform by their 

 proximate fibres being indistinguishably 

 blended: thus the muscles form the most 

 substantial part of the pharynx. The 

 lining membrane, which is of the mu- 

 cous class, is soft and thick in substance, 

 and palely tinged with red in color, and is 

 papillary and in places rugose upon its sur- 

 face ; being perforated by the ducts of 

 numerous follicles which discharge a mucus 

 that preserves glibness and moisture to its 

 interior. The membrane itself is (where it 

 meets them) continuous both with the buc- 

 cal membrane and that which lines the 

 esophagus. 



" Although the pharynx is designed for 

 the reception of the food, it does not open 

 directly into the mouth ; the two cavities 

 are separated from each other by the soft 

 palate and epiglottis. Except in the act of 

 sw^allowing and coughing, they have no 

 communication : in the former case, the 

 velum is pressed upward by the food 

 against the posterior openings of the nose ; 

 in the latter, the larynx is depressed by a 

 convulsive action of the muscles in the 

 vicinity. Into the cavity above the velum 

 there are four openings — two of the cham- 

 bers of the nose, one of the larynx, and one 

 of the esophagus : the eustachian tubes do 

 not open into the pharynx; they end in 

 two large membranous pouches at the 

 upper part of the fauces. The opening 

 leading into the esophagus is constantly 

 closed, except when alimentary matters are 

 passing to or from the stomach ; so that air 

 received into the pharynx through the nose 

 can pass nowhere else but into the wind- 

 pipe ; but if food be returned from the 

 stomach, it will be regurgitated into the 

 nose ; at least, only that portion of it 

 which enters the pharynx at the moment 

 that the larynx is depressed in the act of 



vomiting, can be thrown into the mouth, 

 in the same way that air is in the act of 



coughing. 



" OF THE ESOPHAGUS. 



" The esophagus, or gullet, is the tube 

 through which the food is conducted from 

 the pharynx into the stomach. 



" Course. — It has its beginning from the 

 pharynx, and is there placed at the upper 

 and back part of the larynx, taking the 

 first part of its course above and behind the 

 trachea, between that tube and the cervical 

 vertebra?. Having proceeded a short way 

 down, it inclines to the left, and soon after 

 makes its appearance altogether on the left 

 side of the trachea, and continues so placed 

 during the remainder of its passage down 

 the neck : this explains why we look for the 

 bolus during the act of swallowing on the 

 left, and not on the right side of the ani- 

 mal. In company vvdth the trachea, the 

 esophagus enters the thorax between the 

 first tw^o ribs, at which place, running above 

 that tube, it quits its companion for the 

 superior mediastinum, which ca\dty it 

 traverses below and a little to the right of 

 the posterior aorta. Immediately beneath 

 the decussation of the crura, the esophagus 

 pierces the substance of the diaphragm, 

 and enters the stomach, at a right angle, 

 about the centre of its upper and anterior 

 part. 



" Structure. — The esophagus presents, 

 externally, a strong, red, muscular coat ; in- 

 ternally, one remarkable for its whiteness, 

 which in its nature is cuticular. The mus- 

 cular coat is composed of two orders of 

 fibres — a longitudinal, forming an out- 

 ward layer ; and a circular, an inward 

 layer : the former will shorten the tube, and 

 perhaps dilate it for the reception of food ; 

 the latter, by successive contractions of the 

 canal, wiU transmit the food into the 

 stomach. The second, or internal coat, is 

 called the cuticular, from its analogy to the 

 cuticle of the skin. Although it is contin- 

 uous with the membrane of the pharnyx, 

 it is of a totally different composition : it is 

 thinner, but it is much more compact and 



