DEGLUTITION AND DEFECATION. 147 



made upon the trunk, though the latter are more productive of pain. It was 

 further observed by Dr. Reid, that this effect was produced b*y pinching the 

 pharyngeal branches only ; no irritation of the lingual division being effectual 

 to the purpose. 



193. If, then, the muscles of deglutition are not immediately stimulated to 

 contraction by the Glosso-Pharyngeal nerve, it remains to be inquired, by what 

 nerve the motor influence is conveyed to them from the Medulla Oblongata ; 

 and Dr. Reid has been equally successful in .proving that this function is per- 

 formed by the pharyngeal branches of the Par Vagum. Anatomical examina- 

 tion of their distribution shows that they lose themselves in the musdes of the 

 pharynx ; and whilst no decided indications of suffering can be produced by 

 irritating them, evident contractions are occasioned when the trunk, separated 

 from the brain, is pinched or otherwise stimulated. It appears, however, that 

 neither is the Glosso-Pharyngeal the sole excitor nerve, nor are the pharyn- 

 geal branches of the Par Vagum the sole motor nerves, concerned in deglu- 

 tition ; for after the former has been perfectly divided on each side, the usual 

 movements can still be excited, though with less energy ; and, after the latter 

 have been cut, the animal retains the means of forcing small morsels through 

 the pharynx, by the action of the muscles of the tongue and neck. From a 

 careful examination of the actions of deglutition, and of the influence of various 

 nerves upon them, Dr. Reid draws the following conclusions : The impres- 

 sions are conveyed to the Medulla Oblongata chiefly through the Glosso-Pha- 

 ryngeal, but also along the branches of the Fifth pair distributed upon the 

 fauces, and probably along the branches of the Superior Laryngeal distributed 

 upon the pharynx. The motor influence passes chiefly along the pharyngeal 

 branches of the Vagus ; along the branches of the Hypoglossal, distributed to 

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

 hyoid muscles ; along the motor filaments of the Recurrents, ramifying upon 

 the larynx ; along some of the branches of the Fifth, supplying the elevator 

 muscles of the lower jaw ; along the branches of the Portio Dura, ramifying 

 upon the digastric and stylo-hyoid muscles, and upon the muscles of the lower 

 part of the face ; and probably along some of the branches of the Cervical 

 plexus which unite themselves to the descendens noni. 



194. When the food has been propelled downwards by the pharyngeal 

 muscles as far as their action extends, its further progress through the oeso- 

 phagus is effected by the peristaltic movement of the muscular coat of the tube 

 itself. This movement is not, however, due only to the direct stimulus of the 

 muscular fibre by the pressur^ of the food, as it seems to be in the lower part 

 of the alimentary canal ; for Dr. J. Reid has found, by repeater! experiment, 

 that the continuity of the oesophageal branches of the Par Vagum with the 

 Spinal Cord, is necessary for the rapid propulsion of the food ; so that it can 

 scarcely be doubted, that an impression made upon the mucous surface of the 

 oesophagus, conveyed by the afferent fibres of these nerves to the Medulla 

 Oblongata, and reflected downwards along the motor fibres, is the real cause 

 of the muscular contraction. If the Par Vagum be divided in the rabbit, on 

 each side, above the oesophageal plexus, but below the pharyngeal branches, 

 and the animal be then fed, it is found that the food is delayed in the oeso- 

 phagus, which becomes greatly distended. Further, if the lower extremity 

 of the par vagum be irritated, distinct contractions are seen in the oesophageal 

 tube, proceeding from above downwards, and extending over the cardiac 

 extremity of the stomach. We have here, then, a distinct case of reflex action 

 without sensation, occurring as one of the regular associated movements in 

 the natural condition of the animal body ; and it is very interesting to find this 

 following upon a reflex action with sensation (that of the pharynx), and pre- 

 ceding an action which is altogether unconnected w T ith the Spinal Cord, (that 



