Hirano (1975, 1977) has proposed the concept that the vocal fold has a layer structure, consisting of multiple layers which have different mechanical properties.
The present author studied variations of the layer structure along the length of the vocal fold and age-dependent variations of the layer structure. Futhermore, vas- cular network of the vocal fold was also investigated. The results were summarized as follows: I. Variations of the layer structure along the length of the vocal fold.
1. The layer structure of the vocal fold varies along the length of the vocal fold.
2. The anterior and posterior macula flava are continuations of the intermediate layer of the lamina propria.
3. The cover is the thickest at the middle and becomes thinner towards the anterior and posterior ends of the membraneous portion of the vocal fold. The intermediate layer is very thick near the ends and is the thinnest at the middle of the membraneous portion. II. Age-dependent variations of the layer structure A) Development of the layer structure
1. In a newborn, the entire lamina propria of the mucosa looks uniform in structure.
2. In young children, there are more fibroblasts and less fibrous components in the lamina propria of the mucosa than in adults.
3. Fibers in the vocal ligament are supposed to be chiefly produced by the fibroblasts in the macula f lava and partly by those in the lamina propria of the mucosa.
4. As one grows, the fibrous components of the lamina propria increase and the layer structure of the vocal fold becomes matured after puberty.
B) Aging of the layer structure
1. The cover tends to become thicker with aging.
2. The intermediate layer becomes thinner with aging.
3. The deep layer becomes thicker with aging.III. Vascular network of the vocal fold.
1. The vessels of the free edge of the vocal fold come in from the anterior or the posterior end of the vocal fold.
2. Around the edge of the vocal fold, most vessels run parallel to the longitudinal axis of the vocal fold.
3. At the middle of the membraneous portion, vessels from both ends anastomose with each other to form a network.
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