Dr. Martyn on the Function of the Thyroid Body. 71 
tone than the instrument that most nearly approaches it,—the 
French horn, which is 9 feet, or the ‘“‘ vox humana”’ pipe of a mode- 
rate-sized organ, which is from 4 to 8 feet long. This economy of 
size in the human organ has always been wondered at, but never, 
that I know, explained. Besides the thyroid body, another part, 
the structure of which I shall describe on another occasion, aids in 
this admirable economy. The nearer mechanism of human design 
approaches to perfection, the more it resembles similar structures in 
animal mechanics. The base of all stringed instruments and musical 
boxes is loaded: in most wind instruments the voicing part is thus 
loaded and strengthened, as in the organ pipe, horn, flute, clarionet, 
&c. The bassoon, which in its lower notes approaches the human 
voice, is uncertain and wheezy in tone for want of this provision. 
‘When the thyroid body is small and thin, the voice will be found 
to be small and shrill; when large, the tone will be full and sonorous ; 
‘when it is morbidly enlarged, the voice will be deeper and more 
base ; and when very large, as in bronchocele, the voice will be 
smothered. 
“The compass of the voice is in great part produced by the 
raising and lowering of the larynx, the shortening and lengthening 
of the vocal tube. The thyroid body partakes of this motion, at 
the same time firmly fixing and rendering tense the parts in each 
position. By its change of shape, bulk and density—flattening and 
thinning when the larynx is raised, enlarging and bulging when it 
is lowered—it aids in giving the particular tone or pitch, high and 
acute in the first case, full and deep in the second ; and, in like man- 
ner, by its varying shape, bulk, density, and pressure, it takes a great 
part in producing the wonderful qualities of modulation and expres- 
sion peculiar to the human voice. In animated conversation, decla- 
mation and singing, this may be seen. 
*‘ Its function then appears to be threefold—rendering the slack, 
mobile and flexible vocal organ or tube rigid, tense and inflexible, 
and fit to produce pure tone; by its bulk and density acting as a 
loader and strengthener, making the tone more sonorous, full and 
deep, and thus compensating for want of length and size in the 
organ ; and finally, by its varying shape, bulk, density and pressure, 
furnishing an important aid in producing the inimitable qualities of 
modulation and expression enjoyed by the human voice. 
“ That it is a part of the organ of voice and an important accessory 
in giving it perfection, may be inferred also from its situation on the 
larynx and trachea, and its being supplied by the same nerves—its 
being largest in man, where the voice and speech are perfect—its 
being proportionally larger in women and children than in men, 
their smaller and more mobile organs requiring its peculiar aid. 
Among the lower animals, it is present (at least in a fully developed 
condition) only in the Mammalia, but among them there is a remark- 
able exception in the Cetacea—they have it not, and they have no 
voice, In Birds, which have such great power and modulation of 
voice, the structure of the vocal organ and tube is different from that 
in man, and sufficient in itself to produce these qualities, 
