PNEUMOGASTRIC, OR PAR VAGUM NERVE. 649 



tory, and the circulatory system, and the evident importance of its relations, have ren- 

 dered the literature connected with its physiology somewhat redundant. We do not 

 propose to discuss in full all of the views entertained from time to time with regard to 

 its functions, but shall state merely what seem to be well-ascertained facts, and the most 

 reasonable inferences, where the facts are difficult of demonstration. In treating of the 

 functions of this nerve, we shall be compelled to make constant reference to its anatomy, 

 and for that reason we have described pretty fully in detail most of the important points 

 in its connections and distribution. 



Although the extensive distribution of the pneumogastrics and their importance will 

 necessitate a long discussion of their physiology, we shall endeavor to separate the points 

 to be considered distinctly, and to simplify the subject as much as possible. 



We shall first treat of the general properties of those filaments derived from the true 

 roots of the nerves, and, following them in their course, shall note the properties derived 

 from their connections with other nerves. 



We shall then treat of the properties of the different branches of the nerves, under 

 distinct heads, taking up these branches as they are given off, from above downward. In 

 this, we shall consider first the properties and functions of the auricular branches ; next, 

 the pharyngeal branches, with their influence upon the action of the pharynx in deglu- 

 tition; next, the superior and inferior laryngeal branches, with their relations to the 

 physiology of the larynx ; next, the cardiac branches, with their influence on the move- 

 ments of the heart and the circulation ; next, the pulmonary branches, with the function 

 of the nerves in connection with respiration ; next, the oesophageal branches, in connec- 

 tion with the influence of the nerves upon the action of the O3sophagus, in deglutition ; 

 and finally, the abdominal branches, with the influence of the nerves upon digestion and 

 the functions of the abdominal viscera. By dividing up, in this way, the action of the 

 pneumogastrics, it is hoped that their physiology may be relieved of much of the com- 

 plexity in which it is apparently involved. 



General Properties of the Roots of Origin of tJie Pneumogastrics. All who have oper- 

 ated upon the pneumogastrics in the cervical region in living animals have noted their 

 exceedingly dull sensibility as compared with the ordinary sensory nerves. Bernard, 

 indeed, states that in this region they are generally insensible ; but we have usually found, 

 in dogs at least, that their division is attended with slight evidences of pain. Without 

 citing in detail all the experiments upon this point, it is sufficient to state that some 

 physiologists, on galvanizing or otherwise irritating the roots of the nerves in animals just 

 killed, have noted movements of the muscles of deglutition, of the oesophagus, and of the 

 muscular coats of the stomach. These experiments have led to the opinion that the 

 proper roots of the nerves are motor as well as sensory. It becomes, therefore, a difficult 

 as well as an important point 'to determine whether or not the roots be of themselves 

 exclusively sensory or mixed. In discussing the properties of the roots, we shall rely 

 almost entirely upon direct experiments ; although the arguments drawn from their 

 anatomical characters, in the presence of ganglia and the deep origin of their fibres, 

 point strongly to their sensory character. It is impossible to stimulate the roots, before 

 they have received motor filaments from other nerves, in living animals, and the experi- 

 ments are therefore made upon animals just killed, before the nervous irritability has dis- 

 appeared. If the true roots of the nerves be exclusively sensory, their galvanization in 

 animals just killed should produce, by direct action, no muscular contraction. If the 

 roots contain any motor filaments, contraction of muscles should follow their stimula- 

 tion. The proper physiological conditions in such experiments are the following : 



1. It is necessary to stimulate the roots so that the filaments from the spinal accessory 

 and from other motor nerves are not involved. 



2. It is important to ascertain, provided movements follow such irritation, whether or 

 not they be due to reflex action. 



