of the chest in breathing , speaking, and expression . 291 
It has been long known that irritation of this nerve con- 
vulses the diaphragm, and that cutting it across paralyses 
that muscle. These facts, with the consideration of its course, 
prove it to be a respiratory nerve, and such has been the uni- 
versal opinion. 
But to what purpose should a distinct nerve be sent to the 
diaphragm, if the other muscles, seated externally, and which 
are associated in action with the diaphragm, and as important 
to respiration, were left without a similar tie to unite them 
with each other, and with the organs of the voice ? 
The external respiratory nerve of the thorax (5 Fig. II.) is a 
counterpart of the internal or phrenic nerve. It comes out 
from the 4th and 5th cervical nerves, and often it is connected 
with the phrenic. It diverges somewhat from that nerve, 
because, instead of descending within the chest, it falls over the 
ribs, and descends in a distinct flat trunk upon the outside of the 
chest, to be distributed intirely to the serratus magnus anticus. 
This muscle has nerves from the spinal marrow, because it 
has to combine in the motions of the frame in loco-motion. 
But the long descending nerve is a respiratory nerve ; which 
we may know from its origin, course, and destination ; in 
its origin and course it is like the diaphragmatic nerve, and 
in its destination also, since it is given to a muscle necessary 
to full inspiration. 
I come now to the spinal accessory nerve (Plate XXXI. 
fig. II. 3)* which is more particularly an object in this paper. 
It is called here the superior respiratory nerve of the trunk. 
Experiments may take a colour from the preconceived idea, 
but the accurate investigation of the structure will not deceive 
* Nervus ad par vagum accessorius. 
