908 THE RESPIRATORY SYSTEM. 
wards towards the chest. Again, if the finger is placed on the larynx during deglutition, 
it will be seen that the larynx moves to a very considerable extent. The pharyngeal 
muscles attached to it, and more especially the stylo- pharyngeal muscles, are chiefly 
responsible for bringing about these movements. During singing, changes in the position 
of the larynx may also be noted, a high note being accompanied by a sheht elevation, and 
a low note by a slight depression of the organ. 
The position of the larynx is not the same at all periods of development and growth. 
In the foetus, shortly before birth, it Hes much higher up in the neck. Thus its lower 
border corresponds to the lower border of the fourth cervical vertebra. Its permanent 
position is not reached until the period of puberty is attained (Symington). This descent 
of the larynx has been stated to be due to the rapid and striking growth of the facial part 
of the skull which lies above it (Symington). It is very doubtful, however, if the facial 
growth has any influence in this direction. In the anthropoid ape, in which the face forms 
a much greater part of the skull than in man, and in which, in the transition from the 
infantile to the adult condition, the facial growth is even more striking than in man, the 
larynx occupies a relatively higher position in the neck. In the early stages of growth 
all the thoracic viscera undergo a gradual subsidence. The larynx in its descent follows 
these. Indeed it cannot do otherwise, seeing that the bifurcation of the trachea 
between infancy and puberty moves downwards more than the depth of one thoracic 
vertebra. 
General Construction of the Larynx.—The wall of the larynx is constructed 
upon a somewhat complicated plan. There is a frame-work composed of several 
cartilages. These are connected together at certain points by distinct jomts and- 
also by elastic membranes. Two elastic cords, which stretch in an antero-posterior 
direction from the front to the back wall of the larynx, form the ground-work of 
the true vocal cords. Numerous muscles are likewise present. These operate 
upon the cartilages of the larynx, and thereby not only bring about changes in 
the relative position of the true vocal cords, but also produce different degrees of 
tension of these cords. The cavity of the larynx i is lined with mucous membrane, 
under which, in certain localities, are collected masses of mucous glands. 
CARTILAGES OF THE LARYNX. 
There are three single cartilages and three pairs of cartilages entering into the 
construction of the lary ngeal wall. They are named as follows :-— 
com : Arytenoid. 
| Thyroid. fers : 
4 . Wes fcueing ati ; Cornicula laryneis, or the 
Single cartilages / Cricoid. Paired cartilages - qin - 
S ith nes pane S cartilages of Santorini. 
| Epiglottis. : Sie oe : 
Cuneiform cartilages. 
Thyroid Cartilage (cartilago thyreoidea)—The thyroid cartilage, the largest 
of the laryngeal cartilages, is formed of two quadrilateral plates termed the ale, 
which meet in front at an angle, and become fused along the mesial plane. Behind, 
the alee diverge from each other, and enclose a wide angular space which is open 
behind. The anterior borders of the alee are only fused in their lower parts. Above 
they are separated by a deep, narrow V-shaped median notch, called the incisura 
thyroidea. In the adult male the angle formed by the meeting of the anterior 
borders of the two ale, especially in its upper part, is very projecting, and with the 
margins of the thyroid notch, which les above, constitutes a marked subcutaneous 
prominence in the neck, which receives the name of the pomum Adami. 
The angle which is formed by the meeting of the two ale of the thyroid cartilage varies to 
some extent in different individuals of the same sex , and shows marked differences in the a 
sexes and at different periods of life. In the adult male the av erage angle is said to be 90° 
the adult female it is 120°; whilst in the infant the alee meet in the form of a gentle curve 
convex to the front. 
The posterior border of each ala of the thyroid cartilage is thick and rounded, 
and is prolonged beyond the superior and inferior borders in the form of two slender 
cylindrical processes, termed cornua. The superior cornu is longer than the inferior 
cornu. It is directed upwards, with a slight inclination inwards and backwards, 
and it ends in a rounded extremity, which is joined to the tip of the great cornu of 
