TRANSACTIONS OF THE SECTIONS. 115 
hood, especially those likely to involve the throat. As vaccination in the youn 
is a preventive or modifier of small-pox, so may the knowlege of the condition o: 
the epiglottis act as a safeguard in the treatment of diseases of the throat, more 
particularly in such terrible affections as croup, diphtheria, and the different forms 
of cedema of the larynx from scarlet fever or other disease. 
On Voluntary Closure of the Glottis, independently of the Act of Breathing. 
By Georer D. Gres, M.D., MA., F.GS. 
Voluntary control over the muscles of the larynx has been surmised, but never 
proved. In certain individuals, however, complete voluntary power is possessed 
over the laryngeal muscles ; and this was discovered in the course of some experi- 
ments performed by the author upon his own larynx with the aid of the laryngo- 
scope. They showed that the action of the posterior crico-arytenoid and the 
thyro-arytenoid muscles could be excited at pleasure by the will, without phona- 
tion and independently of the act of respiration; that is to say, breathing was 
interrupted for a few moments, and muscular action induced, the resulting ap- 
pearances being seen in the laryngeal mirror. 
It is considered to be more than probable, nay, almost certain, by some of our 
best physiologists, that all the muscles of the larynx are in a state of action during 
phonation ; and through the general harmony and sympathy which exists every- 
where amongst groups of muscles associated for one common purpose, it is assumed 
with perfect correctness that their states of action and relaxation are adjusted in 
such nicely balanced proportions as to produce the effect required by an education 
and practice of which the will is scarcely cognizant. -A priort, therefore, if volun- 
tary power is possessed over one set of muscles, it must be equally so in neigh- 
bouring groups, because of this harmony and sympathy existing among such 
muscles as those of the larynx in phonation. 
Whilst one group is therefore seen to act through voluntary power, it is but 
reasonable to assume that other groups are simultaneously influenced by the same 
agency ; and this can be proved to be correct. 
In the author’s larynx, if he deeply inspires and forcibly or strongly draws in 
the air, the glottis is seen widely open, the thyro-arytenoid muscles and vocal 
cords are drawn laterally outwards, and under favourable circumstances the trachea 
can be seen throughout its entire length, permitting of a view of its bifurcation and 
commencement of the bronchial tubes. This act is accomplished during breathing 
by the action of the posterior crico-arytenoid muscles. 
If, on the other hand, the breathing is arrested for a few moments, and the 
action of the little muscles excited by the will, there is seen a remarkable pheno- 
menon, which consists in the opening and shutting of the glottis with extreme 
rapidity, in the same manner as the blades of a pair of scissors. 
he glottis may be retained of a triangular shape, perfectly motionless, or kept 
quite shut, the edges remaining in contact, at pleasure. So complete is the con- 
trol over the laryngeal muscles in the author, that the balance of contraction and 
relaxation of the fibres may be so accurately regulated as to retain the glottis of 
any form, size, or width, at will, for some seconds, without an inspiration. 
hen the lips of the glottis are in contact, and so retained, the pressure is such, 
during the muscular contraction, that the fibres of the aryteno-epiglottic or Hil- 
ton’s muscle are set in action, and the epiglottis is drawn downwards, and to some 
extent conceals the glottis. This last phenomenon further proves the voluntary 
power possessed over a set of fibres which were considered as the least likely to be 
under the control of the will, for their action was called spasmodic or convulsive, 
which permitted of the rapid passage of the food over the glottis and its precipita- 
tion into the cesophagus. 
According to Bishop, the posterior crico-arytenoid muscles alone open the 
glottis, while all the rest close it. As the reflection of the voluntary action of the 
thyro-arytenoid muscles can be seen, of necessity the arytenoid and lateral crico- 
arytenoid act at the same moment, and as their fibres relax, those of the posterior 
crico-arytenoid contract, and thus the glottis is opened and shut by the will, 
during the alternate and simultaneous action of these muscles whilst agit 
