774 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 on their surface 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 alee of the thyroid cartilage, and behind to the ante- 

 rior 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- 

 aryta3noideus 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-arytaenoideus muscle. The anterior part of the ventricle 

 leads up by a narrow opening into a ca3cal pouch of mucous membrane of 

 variable size, called the laryngeal pouch. 



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

 the superior vocal cord and the inner surface of the thyroid cartilage, occasion- 

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

 slightly backwards, like a Phrygian cap. On the surface of its mucous mem- 

 brane 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 Arytasno-epiglottideus Inferior muscle (Compressor 

 Sacculi Laryngis, Hilton) ; whilst its exterior is covered by the Thyro-epiglot- 

 tideus muscle. These muscles compress the sacculus laryngis, and discharge 

 the secretion it contains upon the chordas vocales, the surface of which it is 

 intended to lubricate. 



Muscles. The intrinsic muscles of the larynx are eight in number; five of 

 which are the muscles of the chordae vocales and rima glottidis; three are con- 

 nected with the epiglottis. 



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



Crico-thyroid. Arytsenoideus. 



Crico-aryta3noideus Posticus. Thyro-arytasnoideus. 



Crico-arytaenoideus 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 and 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 be- 

 tween the outer border of the posterior surface of the cricoid cartilage, and the posterior margin 

 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 

 about one case in five. 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, which is con- 

 nected to the anterior margin of the horn. 



