708 ORGANS OF VOICE AND RESPIRATION. 



The inferior or true vocal cords, so called from their being concerned in the 

 production of sound, are two strong fibrous bands (inferior thyro-arytenoid liga- 

 ments), covered externally by a thin layer of mucous membrane. Each ligament 

 consists of a band of yellow elastic tissue, attached in front to the depression 

 between the two alae of the thyroid cartilage, and behind to the anterior angle of 

 the base of the arytenoid. Its lower border is continuous with the thin lateral 

 part of the crico-thyroid membrane. Its upper border forms the lower boundary 

 of the ventricle of the larynx. Externally, the Thyro-aryteenoideus muscle lies 

 parallel with it. It is covered internally by mucous membrane, which is extremely 

 thin, and closely adherent to its surface. 



The ventricle of the larynx is an oblong fossa, situated between the superior 

 and inferior vocal cords on each side, and extending nearly their entire length. 

 This fossa is bounded above by the free crescentic edge of the superior vocal 

 cord ; below, by the straight margin of the true vocal cord ; externally, by the 

 corresponding Thyro-arytagnoideus muscle. The anterior part of the ventricle 

 leads up by a narrow opening into a csecal pouch of mucous membrane of variable 

 size, called the laryngeal pouch. 



The sacculus laryngis or laryngeal pouch is a membranous sac, placed between 

 the superior vocal cord and the inner surface of the thyroid cartilage, occasionally 

 extending as far as its upper border ; it is conical in form, and curved slightly 

 backwards, resembling in form a Phrygian cap. On the surface of its mucous 

 membrane are the openings of sixty or seventy small follicular glands, which are 

 lodged in the submucous areolar tissue. This sac is inclosed in a fibrous capsule, 

 continuous below with the superior thyro-arytenoid ligament; its laryngeal 

 surface is covered by the Arytamo-epiglottideus inferior muscle (Compressor sac- 

 culi laryngis, Hilton), whilst its exterior is covered by the Thyro-epiglottideus 

 muscle. These muscles compress the sacculus laryngis, and discharge the secre- 

 tion it contains upon the chords vocales, the surfaces of which it is intended to 

 lubricate. 



MUSCLES OF THE LARYNX. The intrinsic muscles of the larynx are eight in 

 number ; five of which are the muscles of the chords vocales and rima glottidis, 

 and three are connected with the epiglottis. 



The five muscles of the chords vocales and rima glottidis are the 



Crico-thyroid. Arytsenoideus. 



Crico-arytcenoideus posticus. Thyro-arytasnoideus. 



Crico-aryta3noideus lateralis. 



The Crico-thyroid 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 upwards and outwards, to be 

 inserted into the lower and inner borders of the thyroid cartilage ; from near the 

 median line in front, as far back as the inferior cornu. 



The inner borders of these two muscles are separated in the middle line by a 

 triangular interval, occupied by the crico-thyroid membrane. 



The Crico-arytsenoideus posticus arises from the broad depression occupying 

 each lateral half of the posterior surface of the cricoid cartilage ; its fibres pass 

 upwards arid outwards, and converge to be inserted into the outer angle of the 

 base of the arytenoid cartilage. The upper fibres are nearly horizontal, the 

 middle oblique, and the lower almost vertical. 1 



1 Dr. Merkel, of Leipsic, has lately described a muscular slip which occasionally extends 

 between the outer border of the posterior surface of the cricoid cartilage, and the posterior mar- 

 gin of the inferior cornu of the thyroid ; this, he calls the " Musculus kerato-cricoideus." It is 

 not found in every larynx, and when present exists usually only on one side, but is occasionally 

 found on both sides. Mr. Turner (Edinburgh Medical Journal, Feb. 1860) states that it is found 

 in the ratio of 21.8 per cent. Its action is to fix the lower horn of the thyroid cartilage backwards 

 and downwards, opposing in some measure the part of the crico-thyroid muscle connected to the 

 anterior margin of the horn. 



