640 ANIMAL PHYSIOLOGY. 
question to keep the mind of the student open to new or pos- 
sible additional factors in the explanation. 
What are the mechanisms by which voice is produced in 
man? Observation proves that the following are essential: 1. 
A certain amount of tension of the vocal cords (bands), 2 A 
certain degree of approximation of 
their edges. 3. An expiratory blast 
of air. 
It will be noted that these are 
all conditions favorable to the vi- 
bration of the vocal bands. The 
greater the tension the higher the 
pitch; and the more occluded the 
glottic orifice the more effective 
the expiratory blast of air. 
The principle on which the vo- 
cal bands act may be illustrated in 
the simplest way by a well-known 
toy, consisting of an elastic bag tied 
upon a hollow stem of wood, across 
which rubber bands are stretched, 
and the vibration of which caused 
by the air within the distended 
bag gives rise to the note. The stu- 
dent who would really understand 
the mechanism of voice-production 
in man, should not only acquire a 
thorough knowledge of the anato- 
Fic. 475.—Longitudinal section of hu- 
man larynx (after Sappey). 1, ven- 
tricle of larynx ; 2, superior vocal 
cord; 3, inferior vocal cord; 4, aryt- 
enoid cartilage ; 5, section of aryt- 
enoid muscle ; 6, 6, inferior portion 
of cavity of larynx; 7, section of 
osterior part of cricoid cartilage ; 
, section of anterior part of same ; 
9, superior border of cricoid car- 
tilage ; 10, section of thyroid car- 
tilage ; 11, 11, superior portion of 
cavity of larynx ; 12, 13, arytenoid 
gland; 14, 16, epiglottis; 15, 17, 
adipose tissue; 18, section of hyoid 
bone; 19, 19, 20, trachea. 
my of the larynx, especially of its 
muscles and their individual ac- 
tion, but by means of the laryngo- 
scope become familiar with the ap- 
pearances of the glottis and adja- 
cent parts during phonation. The 
latter is not difficult, and auto- 
laryngoscopy or self-examination 
may be made instructive beyond what can be indicated in any 
text-book. 
In order to acquire a knowledge of the human larynx, we 
recommend the dissection of the larynx of a pig, this being 
more like the organ of man than is that of the sheep or most 
other animals. It is especially important to recognize the na- 
ture, extent, and effect on the vocal bands of the movements of 
