1174 THE ORGANS OF VOICE AND RESPIRATION 



about 8 mm. (-^ inch) long, connecting the anterior extremities of the vocal 

 processes, while the inner surfaces of the arytenoids are parallel to each other, 

 and hence the glottis respiratoria is rectangular. During extreme adduction 

 of the cords, as in the emission of a high note, the glottis vocalis is reduced to a 

 linear slit by the apposition of the cords, while the glottis respiratoria is triangular, 

 its apex corresponding to the anterior extremities of the vocal processes of the 

 arytenoids, which are approximated by the inward rotation of the cartilages. 

 Conversely in extreme abduction of the cords, as in forced inspiration, the aryte- 

 noids and their vocal processes are rotated outward, and the glottis respiratoria 

 is triangular in shape, but with its apex directed backward. In this condition 

 the entire glottis is somewhat lozenge-shaped, the sides of the glottis vocalis 

 diverging from before backward, those of the glottis respiratoria diverging from 

 behind forward, the widest part of the aperture corresponding with the attachment 

 of the cords to the vocal processes. 



Muscles of the Larynx. The extrinsic muscles are those which pass between 

 the larynx and parts around these have been described on pages 387 to 389. 

 The intrinsic muscles, confined entirely to the larynx, are: 



Cricothyroideus. Cricoarytenoideus lateralis. 



Cricoarytenoideus posticus. Arytenoideus 



Thyroarytenoideus. 



The Arytenoideus is a single muscle, the other four are paired. 



Dissection. In order to expose the Lateral cricothyroid and Thyroarytenoid muscles 

 the thyroid cartilage of one side must be removed. Begin by taking away the Cricothyroid 

 muscle, then dividing the lateral thyrohyoid ligament; disarticulate the inferior cornu of the 

 thyroid cartilage from the cricoid cartilage, then carefully cut through the thyroid cartilage a 

 short distance from its union with its twin. 



The Cricothyroid (m. cricothyreoideus) (Figs. 888 and 889) is triangular in form, 

 and situated at the fore part and side of the cricoid cartilage. It arises from the 

 front, and lateral part of the cricoid cartilage; its fibres diverge,, passing obliquely 

 upward and outward to be inserted into the "lower border of the thyroid cartilage 

 and into the anterior border of the lower cornu. The inner borders of these 

 two muscles are separated in the middle line by a triangular interval occupied 

 by the central part of the cricothyroid membrane. 



The Posterior Cricoarytenoid (m. cricoarytaenoideus posterior) (Figs. 888 and 889) 

 arises from the broad depression occupying each lateral half of the posterior 

 surface of the cricoid cartilage; its fibres pas's" upward and outward, converging 

 to be inserted into the outer angle (muscular process) of the base of the arytenoid 

 cartilage. The upper fibres are nearly horizontal, the middle oblique, and the 

 lower almost vertical. 



The Lateral Cricoarytenoid (m. cricoarytaenoideus lateralis} (Figs, 888 and 889), 

 a paired muscle, is smaller than the preceding, and of an oblong form. It arises 

 from the upper border of the side of the cricoid cartilage, and, passing obliquely 

 upward and backward, is inserted into the muscular process of the arytenoid 

 cartilage in front of the posterior Cricoarytenoid muscle. The deep surface 

 is applied to the cricothyroid membrane, its external or superficial surface is 

 subjacent to the thyroid cartilage. 



The Arytenoideus (Figs. 888 and 889) is a single muscle filling up the posterior 

 concave surface of the arytenoid cartilages. It arises from the posterior surface 

 and outer border of one arytenoid cartilage, and is inserted into the corre- 

 sponding parts of the opposite cartilage. It consists of three planes of fibres, 

 two oblique and one transverse. The oblique fibres (m. arytenoideus obliquus), 



