596 



COMPARATIVE PHYSIOLOGY, 



Fig. 435, — Illustrates action of thyro-aiytenoideus intemus. 



vocal baads are attached posteriorly, that most of the important 

 changes in the tension, approximation, etc., of the latter are 

 produced. The lungs are to be regarded as the bellows furnish- 

 ing the necessary wind-power to set the vocal bands vibrating, 

 while the larynx has respiratory as well as vocal functions, as 

 has been already learned. Assuming that the student has a 

 good knowledge of the general anatomy of the larynx, we call 

 attention briefly to the following : 



Widening of the glottis is effected by the crico-arytenoideus 

 posticus pulling outward the processus vocalis or attachment 

 posteriorly of the vocal band, and a similar effect is produced 

 by the arytenoideus posticus acting alone. 



Narrowing of the glottis is accomplished by the crico-aryt- 

 enoideus lateralis, and the following when acting either singly 

 (except the arytenoideus posticus), or in concert, as the sphinc- 

 ter of the larynx, viz., the thyro-arytenoideus externus, thyro- 

 arytenoideus intemus, thyro-aryepiglotticus arytenoideus pos- 

 ticus. 



Tension of the vocal bands is brought about by the sphincter 

 group, and especially by the external and internal thyro-aryte- 

 noid muscles. 



Nerve Supply. — The superior laryngeal contains the motor 

 fibers for the crico-thyroid (possibly also the arytenoideus pos- 

 ticus) and also supplies the mucous membrane. The inferior 

 laryngeal supplies all the other muscles. While both of these 

 nerves are derived from the vagus, their fibers really belong to 

 the spinal accessory. It is worthy of note that the entire group 



