122 Analyses of a Series of Papers, by Mr. C. Bell, 



to the sternum or breast-bone, raises or heaves the chest; and 

 the operation of this muscle is very evident in all excited states 

 of respiration, in speaking, and still more in singing, coughing, 

 and sneezing. But there is something necessary to the full 

 effect of this muscle on the chest; for otherwise it will be a 

 muscle of the head, and not of the chest. 



2. The trapezius must fix the head or pull it backwards be- 

 fore the mastoideus can act as a respiratory muscle ; and how 

 they are combined we shall presently see. 



The position of the head of the asthmatic during the fit, as well 

 as the posture of the wounded or the dying, proves the influence 

 of the upper part of the trapezius in excited respiration. 



3. The serratus magnus anticus, being extended over the 

 whole side of the chest, and attached in all the extent from 

 the 2d to the 8th rib, is very powerful in raising the ribs ; but 

 it cannot exert this power independently of the trapezius; 

 since, without its combination, its force would be exerted in 

 moving the scapula, and not the ribs : unless the scapula be 

 fixed, or pulled back by the trapezius, the serratus is not a 

 muscle of respiration. 



In this maimer do these three powerful muscles hang to- 

 gether in their action, combining with the diaphragm to en- 

 large the cavity of the chest in all its diameters ; and to these 

 muscles are distributed in a peculiar manner the nerves which 

 may thence appropriately be termed the respiratory nerves of 

 the chest. 



The Anatomy of the respiratory Nerves of the Trunk. 



1. The phrenic takes its origin or proceeds from the fourth 

 cervical nerve, a more slender branch joining it from the 

 third cervical ; it also has connexions with the ncrvus vagus, 

 the lingualis mcdius, and at the same time gives off a branch 

 to the larynx. Its trunk descends into the cavity of the 

 thorax, giving off no branches till it diverges and disperses 

 itself in the substance of that muscle : the irritation of this 

 nerve convulses the diaphragm, and cutting it across paralyses 

 it ; the connexions moreover which we have enumerated would 

 mark its relations. 



2. The external respiratory nerve of the thorax is a counter- 

 part of the former, or internal respiratory; it proceeds from 

 the 4th and 5th cervical, like the phrenic, and is often con- 

 nected with it. This nerve descends as a distinct flat trunk 

 upon the outside of the chest to be distributed exclusively to 

 the serratus magnus anticus. This muscle has nerves coming 

 to it from the spinal marrow besides, because it has to com- 

 bine 



