**2.1 Structure of the vocal fold**

Current voice microsurgery techniques are based on Hirano's discovery of the layered structure of the vocal folds (Hirano 1974; Bleach, Milford et al. 1997; James B. Snow and Ballenger 2003). Based on his microscopic work, the vocal fold was found to have three well defined layers - the epithelium, lamina propria and vocalis muscle. The lamina propria was further subdivided into 3 layers, the superficial layer of the lamina propria (SLLP), intermediate layer and deep layer.

In the SLLP, elastin and collagen fibres are loosely arranged within a matrix, whereas dense elastin fibres make up most of the intermediate layer. Collagen is densely packed in the deep layer, providing most of the support for the lamina propria (James B. Snow and Ballenger 2003). Hirano also proposed a cover-body concept, providing an explanation for the vibratory characteristics of the vocal fold. Based on his theory, the cover (consisting of stratified squamous epithelium and the underlying SLLP) is attached to the body (consisting of the vocalis and thyroarytenoid muscles) by an elastic interface or ligament (composed of the intermediate and deep layers of the lamina propria), with an increasing stiffness from superficial to deep. This allows the cover to oscillate independently due to its elastic characteristics, resulting in the mucosal wave seen on stroboscopy and most of the vibratory dynamics required for good voice production and phonation (Hirano 1974).
