308 NERVES CONCERNED IN DEGLUTITION. 



Within the esophagus, whose stratified epithelium is moistened with 

 the mucus derived from the mucous glands in its walls, the downward 

 movement is involuntary, and depends upon a complicated reflex 

 movement discharged from the centre for deglutition there is a peri- 

 staltic movement of the outer longitudinal and inner circular non- 

 striped muscular fibres. 



In the upper part of the oesophagus which contains striped muscular fibres, the 

 peristalsis takes place more quickly than in the lower part. The movements of 

 the oesophagus never occur independently, but are always the continuation of a 

 foregoing act of deglutition. If food be introduced into the oesophagus through a 

 hole in its wall, there it lies; and it is only carried downwards when a movement 

 to swallow is maole (Volkmann). The peristalsis extends along the whole length 

 of the oesophagus, even when it is ligatured or when a part of it is removed 

 (Mosso). If a olog be allowed to swallow a piece of flesh tieol to a string, so that 

 the flesh goes half-way down the oesophagus, and if the flesh be witholrawn, the 

 peristalsis still passes downwards (G. Ludwig anol Wild). 



The motor nerve of the oesophagus is the vagus (not the accessory fibres) ; after it 

 is olivioled, the food lodges in the lower part of the oesophagus. Very large and 

 very small masses are swallowed with more difficulty than those of moderate size. 

 Dogs can swallow an olive-shaped body weighted with a counterpoise of 450 

 grammes (Mosso). When the thorax is greatly distended, as in Miiller's experi- 

 ment, or greatly diminished, as in Valsalva's experiment (p. 112), deglutition is 

 rendered more difficult. 



Goltz observed, that the oesophagus and stomach (frog) became greatly more 

 excitable, i.e., the excitability of the ganglionic plexuses in their walls was 

 increased, when the brain and spinal corol or both vagi were destroyed. These 

 organs contracted energetically after slight stimulation, while frogs whose cen- 

 tral nervous system was intact, swallowed fluids simply by peristalsis. Females, 

 and sometimes men also, with marked weakening of the nervoiis system 

 (Hysteria), not unfrequently have similar spasmodic contractions of the cesophageal 

 region (globus hystcricus). After section of both vagi, Schiff observed spasmodic 

 contraction of the oesophagus. 



[Structure of the (Esophagus. The walls of the oesophagus are 

 composed of three coats mucous, sub-mucous, and muscular. 



The mucous coat is firm and is thrown into longitudinal folds, which 

 disappear when the tube is distended. It is lined by several layers of 

 stratified squamous epithelium. The membrane itself is composed, 

 especially at its inner part, of dense fibrous tissue, which projects in 

 the form of papillre, into the stratified epithelium. At its outer part 

 is a continuous layer of non-striped muscle, the muscularis mucoscc. 



The sub-mucous coat is thicker than the foregoing, and consists of 

 loose connective-tissue, with the acini of small compound tubular 

 mucous glands imbedded in it. The ducts pierce the muscularis 

 mucosse to open on the inner surface of the tube. 



The muscular coat consists of an inner, thicker, circular, and an outer, 

 thinner, longitudinal layer of non-striped muscle. In man, the upper 

 third of the gullet consists of striped muscular fibres. Outside the 

 muscular coat is a layer of fibrous tissue with elastic fibres. 



