1062 THE EESPIKATOEY SYSTEM. 



it is more deeply placed. There, it is overlapped by the sterno-cleido-mastoid muscle, 

 and is covered by the two strata of thin ribbon-like muscles which are attached to 

 the thyreoid cartilage and the hyoid bone ; and it is hidden, to some extent, by the 

 upper prolongations of the lateral lobe.s of the thyreoid gland. 



The position of the larnyx is influenced by movements of the head and neck. Thus 

 it is elevated or raised when the head moves dorsally, and depressed when the chin 

 is carried downwards towards the chest. Again, if the finger is placed upon it during 

 deglutition, it will be noted 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 slight 

 upward movement, and a low note by a similarly slight downward movement 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 lies much nearer the head, and its inferior border 

 corresponds to the inferior border of the fourth cervical vertebra. Its permanent position 

 is not reached until the period of puberty is attained (Symington). This downward 

 movement of the larynx has been stated to be due to the rapid and striking growth of 

 the facial part of the skull (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 it 

 is 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 and the larynx 

 follows them. Indeed, it cannot do otherwise, seeing that the bifurcation of the 

 trachea between infancy and puberty moves downwards towards the caudal end of 

 the body 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 framework composed of several 

 cartilages. These are connected together, at certain points, by distinct joints and 

 also by elastic membranes. Two elastic cords, which stretch in a ventro-dorsal 

 direction from the ventral to the dorsal wall of the larynx, form the groundwork 

 of the vocal folds (O.T. true vocal cords). Numerous muscles also are present. 

 These operate upon the cartilages of the larynx, and thereby not only bring about! 

 changes in the relative position of the vocal folds, but also produce different 

 degrees of tension of these folds. The cavity of the larynx is lined with mucougj 

 membrane, under which, in certain localities, are collected masses of mucous glands. 



CARTILAGINES LARYNGIS. 



Three single cartilages and three pairs of cartilages enter into the constructor 

 of the laryngeal wall. They are named as follows : 



/ mi -j ( Aryteenoids. 



Single cartilages \ Cricokl! ' Paired cartilages \ ^""l^ 



( Epiglottis. ( cuneiform eartilagw. 



Cartilago Thyreoidea. The thyreoid cartilage, the largest of the laryngea 

 cartilages, is formed of two quadrilateral plates termed the laminae, which mee 

 ventrally at an angle, and become fused along the median plane. Dorsally th 

 laminae diverge from each other, and enclose a wide angular space which is opei 

 dorsally. The ventral borders of the laminae are fused only in their inferior parts 

 Above they are separated by a deep, narrow V-shaped median notch, called th 

 incisura thyreoidea or thyreoid notch. In the adult male the angle formed by th 

 meeting of the ventral borders of the two laminae, especially in its upper part, i 

 very projecting, and with the margins of the thyreoid notch, which lies abov( 

 constitutes a marked subcutaneous prominence in the neck, which receives th' 

 name of the prominentia laryngea (O.T. Adam's Apple). 



