PXEUMOGASTBIC NERVE. 463 



cavity of the chest. It curves round the subclavian artery on the 

 right side and the arch of the aorta on the left, and ascends in the 

 groove between the trachea and oesophagus, to the larynx. It 

 then enters the larynx between the cricoid cartilage and the pos- 

 terior edge of the thyroid, and is distributed to all the muscles of 

 the larynx, with the exception of the crico- thyroid. This brand i 

 is, therefore, exclusively muscular in its distribution. 



The trunk of the pneumogastric, after supplying the above 

 branches, as well as sending numerous filaments to the trachea 

 and oesophagus in the neck, gives off in the chest its pulmonary 

 branches, which follow the bronchial tubes in the lungs to their 

 minutest ramifications. It then passes into the abdomen and sup- 

 plies the muscular and mucous layers of the stomach, ramifying 

 over both the anterior and posterior surfaces of the organ ; after 

 which its fibres spread out and are distributed to the liver, spleen, 

 pancreas, and gall-bladder. 



The functions of the pneumogastric will now be successively 

 studied in the various organs to which it is distributed. 



Pharynx and (Esophagus. The reflex action of deglutition, which 

 has already been described as commencing in the upper part of the 

 pharynx, by means of the glosso-pharyngeal, is continued in the 

 lower portion of the pharynx and throughout the oesophagus by 

 the aid of the pneumogastric. As the food is compressed by the 

 superior constrictor muscle of the pharynx and forced downward, 

 it excites the mucous membrane with which it is brought in contact 

 and gives rise to another contraction of the middle constrictor. The 

 lower constrictor is then brought into action in its turn in a similar 

 manner ; and a wave-like or peristaltic contraction is thence pro- 

 pagated throughout the entire length of the oesophagus, by which 

 the food is carried rapidly from above downward, and conducted at 

 last to the stomach. Each successive portion of the mucous mem- 

 brane, in this instance, receives in turn the stimulus of the food, 

 and excites instantly its own muscles to contraction ; so that the 

 food passes rapidly from one end of the oesophagus to the other, by 

 an action which is wholly reflex in character and entirely withdrawn 

 from the control of the will. Section of the pneumogastric, or of 

 its pharyngeal and cesophageal branches, destroys therefore at the 

 same time the sensibility and the motive power of these parts. The 

 food is no longer conveyed readily to the stomach, but accumulates 

 in the paralyzed oesophagus, into which it is forced by the voluntary 



