on the Structure, Distribution, and Functions of the Nerves. 121 



the sulci, that give rise to the anterior and posterior roots 

 of the spinal nerves. From this narrow medullary column 

 arise in succession from above downwards, the portio dura 

 of the 7th nerve ; the glosso-pharijngeus nerve ; the nerve 

 of thenar vagum ; the nervus ad par vagum accessor ius; the 

 phrenic and the external respiratory nerves : these latter 

 nerves, though coming out with the cervical, do in all proba- 

 bility take their origin from the same portion of the medidla 

 spinalis with the accessory nerve. With regard to the inter- 

 costal nerves, or those which actuate the intercostal muscles, 

 they by their relations with the medulla oblongata are equal 

 to the performance of respiration as it regards the office of 

 the lungs ; but they are not adequate to those additional func- 

 tions which are in a manner imposed upon the respiratory ap- 

 paratus, when they are brought to combine in other offices. 



Of the Muscles of the Trunk, "which are brought in aid of the 

 common respiratory Muscles. 



It is not difficult to discover what muscles are best calcu- 

 lated by their situation and direction to assist in the motions of 

 the chest, when there is increased or excited action ; nor less 

 so to assign a use to the nerves which supply these muscles 

 exclusively. These nerves are not only remarkble on this ac- 

 count, but also from their having the same origin. 



In this inquiry it is necessary to observe, that the life of 

 animals is protected by a particular sense which gives rise to 

 an instinctive motion of drawing the breath, by which the chest 

 is suddenly and powerfully expanded, on exertion or alarm. 

 The start on sudden alarm is accompanied with a rapid ex- 

 pansion and rising of the chest; and the voice, at such a 

 moment, is produced by suddenly inhaling, and not by ex- 

 piration ; and this expansion of the chest combines with the 

 preparation for flight or defence, since the extension of the 

 muscles lying on the breast and back is produced by this mo- 

 tion, and since they are thereby rendered more powerful in 

 their influence upon the arms or anterior extremities. 



It cannot escape observation that oppression and difficulty 

 of breathing is exhibited in gasping and forcible inspiration, in 

 drawing the breath, not in throwing it out : accordingly we 

 find that the muscles above alluded to are powerfully in- 

 fluenced in deep inspiration, whether the action be voluntary 

 as in speech, or involuntary as in the last efforts of life, when 

 sense is lost; they are the mastoid muscle, the trapezius, the 

 terrains magnus, and the diaphragm. 



1. Sterno-clcido-mastoidais. Tl lis muscle by being attached 

 Vol.64. No. 316. Jug. 1824. Q to 



