THE LARYNX2
At the point of junction of the two halves of the cartilage on either side, is a small round elevation, for articulation with the inferior cornu of the thyroid cartilage.
The lower border of the cricoid cartilage is horizontal, and connected to the upper ring of the trachea by fibrous membrane.
Its upper border is directed obliquely upwards and backwards, owing to the great depth of its posterior surface. It gives attachment, in front, to the crico-thyroid membrane; at the sides, to part of the same membrane and to the lateral Crico-arytenoid muscle; behind, the highest point of the upper border is surmounted on each side by a smooth oval surface, for articulation with the arytenoid cartilage. Between the articular surfaces is a slight notch, for the attachment of part of the Arytenoideus muscle.
The inner surface of the cricoid cartilage is smooth, and lined by mucous membrane.
The Arytenoid Cartilages are so called from the resemblance they bear, when approximated, to the mouth of a pitcher . They are two in number, and situated at the upper border of the cricoid cartilage, at the back of the larynx. Each cartilage is pyramidal in form, and presents for examination three surfaces, a base, and an apex.
The posterior surface is triangular, smooth, concave, and lodges part of the Arytenoideus muscle.
The anterior surface, somewhat convex and rough, gives attachment to the Thyro-arytenoid muscle, and to the false vocal cord.
The internal surface is narrow, smooth, and flattened, covered by mucous membrane, and lies almost in apposition with the cartilage of the opposite side.
The base of each cartilage is broad, and presents a concave smooth surface, for articulation with the cricoid cartilage. Of its three angles, the external one is short, rounded, and prominent, receiving the insertion of the posterior and lateral Crico-arytenoid muscles. The anterior one, also prominent, but more pointed, gives attachment to the true vocal cord.
The apex of each cartilage is pointed, curved backwards and inwards, and surmounted by a small conical-shaped, cartilaginous nodule, corniculum laryngis (cartilage of Santorini). This cartilage is sometimes united to the arytenoid, and serves to prolong it backwards and inwards. To it is attached the aryteno-epiglottidean fold.
The Cuneiform Cartilages (cartilages of Wrisberg) are two small, elongated, cartilaginous bodies, placed one on each side, in the fold of mucous membrane which extends from the apex of the arytenoid cartilage to the side of the epiglottis (aryteno-epiglottidean fold); they give rise to the small whitish elevations on the inner surface of the mucous membrane, just in front of the arytenoid cartilages.
The Epiglottis is a thin lamella of fibro-cartilage, of a yellowish colour, shaped like a leaf, and placed behind the tongue and in front of the superior opening of the larynx. During respiration, its direction is vertically upwards, its free extremity curving forwards towards the base of the tongue; but when the larynx is drawn up beneath the base of the tongue during deglutition, it is carried downwards and backwards, so as to completely close th'e opening of the larynx. Its free extremity is broad and rounded; its attached end is long and narrow, and connected to the receding angle between the 1\»-o ate of the thyroid cartilage, just below the median notch, by a long, narrow, ligamentous band, the thyro-epiglottic ligament. It is also connected to the posterior surface of the body of the hyoicl bone, by an elastic ligamentous band, the hyo-epiglottic ligament.
Its anterior or lingual surface is curved forwards towards the tongue, and covered by mucous membrane, which is reflected on to the sides and base of this organ, forming a median and two lateral folds, the
glosso-epiglottidean ligaments.
Its posterior or laryngeal surface is smooth, concave from side to side, convex from above downwards, and covered by mucous membrane; when this is removed, the surface of the cartilage is seen to be studded with a number of small mucous glands, which are lodged in little pits upon its surface. To its sides the aryteno-epiglottidean folds are attached.
Structure. The epiglottis, cuneiform cartilages, and cornicula laryngis are composed of yellow cartilage, which shows little tendency to ossification; but the other cartilages resemble in structure the costal cartilages, and they become more or less ossified in old age.
Ligaments. The ligaments of the larynx are extrinsic, as those connecting the thyroid cartilage with the os hyoides; and intrinsic, as those connecting the several cartilaginous segments to each other.
The ligaments connecting the thyroid cartilage with the os hyoides, are thrpo in number; the thyro-hyoidean membrane, and the two lateral thyro-hyoidean ligaments.
The Thyro-hyoidean Membrane is a broad, fibro-elastic, membranous layer, attached below to the upper border of the thyroid cartilage, and above to the upper border of the inner surface of the hyoid bone; being separated from the posterior surface of the hyoid bone by a synovial bursa. It is thicker in the middle line than at either side, in which situation it is pierced by the superior laryngeal nerve and artery.
The two lateral Thyro-hyoidean Ligaments are rounded, elastic cords, which pass between the superior cornua of the thyroid cartilage, to the extremities of the greater cornua of the hyoid bone. A small cartilaginous nodule (cartilage triticea), sometimes bony, is found in each.
The ligaments connecting the thyroid cartilage to the cricoid are also three in number; the crico-thyroidean membrane, and the capsular ligaments and synovial membrane.
The Crico-thyroid Membrane is composed mainly of yellow elastic tissue. It is of triangular shape; thick in front, where it connects together the contiguous margins of the thyroid and cricoid cartilages; thinner at each side, where it extends from the superior border of the cricoid cartilage, to the inferior margin of the true vocal cords, with which it is closely united in front.
The anterior portion of the crico-thyroid membrane is convex, concealed on each side by the Crico-thyroid muscle, subcutaneous in the middle line, and crossed horizontally by a small anastomotic arterial arch, formed by the junction of the crico-thyroid branches on either side.
The lateral portions are lined internally by mucous membrane, and covered by the lateral Crico-arytenoid and Thyro-arytenoid muscles.
A Capsular Ligament encloses the articulation of the inferior eornu of the thyroid with the side of the cricoid, on each side. The articulation is lined internally by synovial membrane.
The ligaments connecting the arytenoid cartilages to the cricoid, are two thin and loose capsular ligaments connecting together the articulating surfaces, lined internally by synovial membrane, and strengthened behind by a strong posterior crico-arytenoid ligament, which extends from the cricoid to the inner and back part of the base of the arytenoid cartilage.
The ligaments of the epiglottis are the hyo-epiglottic, the thyro-epiglottic, and the three glosso-epiglottic folds of mucous membrane which connect the epiglottis to the sides and base of the tongue. The latter have been already described.
The Hyo-epiglottic Ligament is an elastic fibrous band, which extends from the anterior surface of the epiglottis, near its apex, to the posterior surface of the body of the hyoid bone.
The Thyro-epiglottic Ligament is a long, slender elastic cord, which connects the apex of the epiglottis with the receding angle of the thyroid cartilage, immediately beneath the median notch, above the attachment of the vocal cords.
Interior of the Larynx. The superior aperture of tlie larynx is a triangular or cordiform opening, wide in front, narrow behind, and sloping obliquely downwards and backwards. It is bounded in front by the epiglottis; behind, by the apices of the arytenoid cartilages, and the cornicula laryngis; and laterally, by a fold of mucous membrane, enclosing ligamentous and muscular fibres, stretched between the sides of the epiglottis and the apex of the arytenoid cartilage: these are the aryteno-epiglottideau folds, on the margins of which the cuneiform cartilages form a more or less distinct whitish prominence.
The cavity of the larynx is divided into two parts by the projection inwards of the chorda? vocales, and Thyro-arytenoid muscles; between the two cords is a long and narrow triangular fissure or chink, the glottis, or
rima glottidis. The portion of the cavity of the larynx above the glottis, is broad and triangular in shape above, and corresponds to the interval between the alas of the thyroid Cartilage; the portion below tin; glottis is at first elliptical, and lower down of a circular form.
The- glottis is the interval between the inferior vocal cords. The two superior or false: vocal cords are placed above the latter, and formed almost entirely by a folding inwards of the mucous membrane; whilst the two inferior or true vocal cords are thick, strong, and formed partly by mucous membrane, and partly by ligamentous fibres. Between the true and false vocal cords, on each side, is tin
oval depression, the sinus or ventricle of the larynx, which leads upwards, oil the outer side of the superior vocal cord, into a caecal pouch of variable size, the sacculus larynffis.
