on the Structure, Distribution, and Functions of the Nerves. 125 



and the latter in raising the chest; and this is confirmed by an 

 experiment consisting in the division of the superior respira- 

 tory nerves of the ass during the time of excited respiration, 

 the consequence of which is the cessation of the increased 

 respiratory action, and relaxation of the sterno-maxillaris 

 and sterno-vertebralis muscles, which answer to the mastoid in 

 man ; and this relaxation continues until the animal brings 

 them into action as voluntary muscles. 



An ass being thrown, its phrenic nerves were divided, on 

 which a remarkable heaving of the chest took place. It rose 

 higher, and the margins of the chest were more expanded at 

 each respiration. There was no particular excitement of the 

 muscles of the neck, shoulder, or throat, at this time; so that 

 to excite the actions of these muscles, it was necessary to com- 

 press the nostrils. When they began to act with more vio- 

 lence, keeping time with the actions of the other muscles of 

 respiration, the superior respiratory nerve was divided ; im- 

 mediately the action ceased in the muscles attached to the 

 sternum of the side where the nerve was divided, while the 

 corresponding muscles of the other side continued their ac- 

 tions. 



It is well known that on the division of the spinal marrow 

 between the cervical and dorsal vertebrae, the respiration is 

 continued by the diaphragm. The phrenic nerves being first 

 divided, and then the spinal marrow cut across at the bottom 

 of the cervical vertebrae, respiration was stopped in the chest; 

 but there continued a catching and strong action at regular 

 intervals in the muscles of the nostrils, face, and side of the 

 neck. These actions ceased also after a time, but were re- 

 newed upon reanimating the animal by artificial breathing, 

 which was done several times, the animal however remaining 

 insensible. 



This class of nerves indicated, by stimulating them after 

 death, a power of retaining their life the longest. 



To avoid the unnecessary repetition of experiments, the 

 author states the facts which have been ascertained by the 

 exertions of others respecting the remaining nerves of this 

 class. Thus the voice is destroyed by dividing the recurrent 

 branch of the par vagum. The consent of motion between 

 the muscles of the glottis and those of the chest, is lost by the 

 division of the laryngeal branch of the par vagum. An in- 

 jury of the ]>ar vagum produces difficulty of breathing. 



Although the regular succession of spinal nerves be equal 

 to the raising and depressing the thorax, and essential to re- 

 spiration, still they are not competent to the performance of 

 the motions of the glottis, pharynx, lips, and nostrils; which 



several 



