28 6 Mr. Bell on the nerves which associate the muscles 
5. The organs of the sense of smelling, and particularly 
the muscles which move the cartilages of the nose, are, in 
their exercise, as necessarily joined to the act of inspiration, 
as those of speech are to the act of expiration. 
6. The powers of the arms in voluntary exertion, are 
in a great measure dependent upon the expansion of the tho- 
rax ; so that the act of inspiration is always combined with 
sudden and powerful exertion. The more indeed we attend 
to the motions of the frame, whether in efforts of strength, or 
in the act of respiration, the more remarkable will the un- 
expected combinations of the muscles appear. 
It is only when we are made sensible of the extent of the 
respiratory actions, and that they in effect extend over the 
whole face and neck and trunk, that we can comprehend how 
the mechanism of the thorax, or rather of the respiratory 
apparatus generally, affects the arrangement of the whole 
nervous system. Wherever, in examining the comparative 
anatomy of animals, we find ribs rising and falling by re- 
spiratory muscles, we have a medulla spinalis , and the distinc- 
tion of cerebrum and cerebellum. And experiment and obser- 
vation prove, that the seat of that power which controuls the 
extended act of respiration, is in the lateral portions of the 
medulla oblongata, from which it is continued through certain 
respiratory nerves which pass out from the neck, and also 
downwards, by corresponding columns of the spinal marrow, 
to the intercostal nerves. 
Origins of the respiratory nerves. 
The nerves on which the associated actions of respiration de- 
pend, and which have been proved to belong to this system, by 
