562 
MR. BISHOP ON THE PHYSIOLOGY 
other transverse. The first of these comprises the muscles which elevate and depress 
the larynx ; the latter, the cartilaginous segments of rings perpendicular to the axis 
of the tube having muscular fibres attached to their posterior extremities, the con- 
traction and elongation of which regulate the diameter of the trachea. The pharynx, 
mouth and nasal cavities, which form the superior extremity of the vocal tube, are 
also provided with muscles to modify the tension of that part of the tube so that it 
may vibrate synchronously with the rest. The necessity for this change in the dimen- 
sions of the tube, in order that it may vibrate in unison with the glottis, is in accord- 
ance, not only with the joint system of pipe and reed above described, but also with 
what actually takes place in the vocal organs of living animals. When the voice is 
raised in the scale from grave to acute, a corresponding elevation takes place in the 
larynx towards the base of the cranium. By placing the finger on the pomum Adami 
this motion can be easily felt, and at the same time the thyroid cartilage is drawn 
up within the os-hyoides, and presses on the epiglottis ; the small space between the 
thyroid and cricoid closes, the pharynx is contracted, the velum palati is depressed 
and curved forward, and the tonsils approach each other : the reverse of these phe- 
nomena takes place during the descent of the voice. These are the principal pheno- 
mena common to most Mammalia which can be recognised by external observation, 
the other changes being, on account of their situation, invisible. 
The effects of these variations on the tone of the voice have been hitherto little 
understood. It has always appeared incomprehensible why the vocal tube should 
apparently increase in length in the production of the acute tones, and shorten in the 
grave ; a circumstance which theoretically presents an acoustic paradox. Dodart 
and many others have conceived the elevation of the larynx to be merely for the pur- 
pose of shortening the vocal tube in the supra-laryngeal cavity, and have considered 
the trachea as producing no effect on the pitch of the tone. M. Majendie has also 
pointed out the shortening of this part of the tube. In order to ascertain the effect 
of these changes, the following experiments were made on the dead body. Having 
laid bare the vocal organs of an adult male, I raised the larynx to the position it 
would occupy by the elevation of the voice to an octave, being about half an inch, 
and at the same time minutely observed the position of the lowest ring of the trachea 
in reference to the sternum. By this operation I found the trachea was raised out 
of the chest, nearly to the same extent as the larynx had been elevated towards the 
base of the skull. The next step was to examine whether any change had taken 
place in the diameter of the tube. For this purpose, having measured the diameter 
of the trachea in its natural position, the larynx was again elevated to the same ex- 
tent as before, when the diameter was found diminished one-third. These experiments 
prove that, contrary to the general preconception, the elevation of the larynx shortens 
the tube independently of the contraction between the thyroid cartilage and os-hyoides, 
and at the same time lessens its diameter. The same effects may easily be detected 
during life by placing the finger on the trachea immediately above the sternum 
