70 Royal Soctety :— 
structure of the thyroid body, its large supply of blood and its capa- 
bility of sudden alterations of bulk ; the author briefly adverts to the 
unsatisfactory explanations which have been offered as to its function, 
and then proceeds to state his own views, as follows :— 
The upper part of the trachea, the larynx, and the passage of the 
fauces and mouth constitute the organ of voice; the two former are 
the essential or voicing part as mechanicians call it, that which pro- 
duces the tone. The larynx and trachea—taking a share in other 
functions and being associated by juxtaposition and attachment with 
contiguous organs—are always pervious and open for respiration ; 
lengthen and shorten, fall and rise with the cesophagus in deglutition, 
and bend and turn with the universal motions of the head and neck. 
«To admit of this great mobility and flexibility, a certain structure 
is necessary. The larynx is a triangular box enclosing the apparatus 
of the chorde vocales ; its two cartilaginous sides or ale, diverging 
from the front, are not fixed but free at the back, being completed 
by soft parts: the trachea is composed of a succession of incomplete 
cartilaginous hoops or rings lying apart, the back and intervals being 
made up and the tube completed by soft membrane. 
“Now the structure of a wind instrument, such as that of the 
human voice is, requires the very opposite properties. It must be 
rigid, tense and inflexible. The qualities of the tone will be in exact 
proportion to these properties. How then is the soft, slack and 
flexible vocal tube rendered thus rigid, tense and inflexible, and fit to 
produce pure tone? The muscles of the larynx, the thyro-hyoid and 
sterno-thyroid, merely raise or lower, or fix it in any position: not 
lying on, or being parallel to, but diverging from the vocal tube, they 
cannot effect the object referred to. It appears to me that the 
thyroid body is provided for this purpose. The act of uttering a” 
tone or of speaking stops the return of the blood from that organ, 
distends and renders it tense, and from the nature of its attachment 
round the top of the trachea and on the free sides of the alee of the 
larynx, renders them fixed, firm, and tense also. This effect is aided 
by the aforesaid muscles, the thyroid body being interposed and 
giving them more advantageous mechanical action. This tension 
may be in any degree, and on energetic speaking or singing, the in- 
creased size of the part and the fulness of the collateral veins may 
be seen. ‘This is the reason of its large supply and free distribution 
of blood. An instance of the want of this tension in an instrument 
may be seen in the bagpipe, where the porte-vent is attached to the 
chanter or voicing part by a flexible joint or by leather, and the tone 
is in consequence squeaking and uncertain. 
“« Besides thus giving rigidity, firmness and tension to the organ 
of voice, the thyroid body also acts in another capacity—as a loader. 
In most musical instruments, loaders are used to render the vibra- 
tions slower and longer, and the tone in consequence fuller, louder 
and deeper. They compensate for want of size and space, and give to 
asmall instrument, or to a small vibrating or voicing part of an instru- 
ment, the power and quality of a large one, The human organ of 
yoice is 8 inches long, and has the same power and better quality of 
