COMPARATIVE HISTOLOGICAL DATA BETWEEN THE VOCAL FOLDS OF HUMANS AND BONOBO

摘要

Histological aspects of primate vocal folds are important for understanding differences vocal functions between species. It has been claimed that vocal folds are more tensed and that the thyro-arytheno?d muscle is stiffer for non-human primates. Hirano (1991) claimed that the arrangement of the tissues in the cover layer of the monkey is different in other mammals and adult mans and that the mucosa is stiffer than in humans or in dogs. One important fact from a comparative and evolutionary perspective is that Hirano's (1974, 1991) seminal description of vocal folds has not been extended yet to other non-human primates. Human vocal folds consist of a body layer (thyro-aryteno?d muscle) and a cover layer (epithelium and lamina propria). Inside the larynx, the fundamental role played by the crico-arytheno?d muscle has not been extended to non-human primates. No extensive investigation of the molecular and cellular structure of the non-human primate vocal folds has been done despite the importance of the subject (Sch?n Ybarra 1995). The arrangement of elastic and collagenous fibers immediately under the epithelium makes the mucosa stiffer in monkeys than in human or dog (Sch?n Ybarra 1995). The paper presents results of a study made on the vocal folds of an adult female Bonobo. Two types of staining (similar to Hirano's for humans) i.e. Hematoxyn-Eosin and Elastica Van Gieson have been made. Coronal slices were dissected at anterior, medial and posterior locations in the vocal folds. Results show that globally the structure of the vocal folds is identical between Bonobo and humans (Pseudo stratified ciliated epithelium of respiratory type). The ventricle is larger for Bonobo, likely due to their connection to the air sacks that do not exist for man. The false vocals folds are more prominent for Bonobo. Reinke's space and the elastic cone are bigger in Bonobo than in man. Malpighian metaplasy suggests that there was much contact between the vocal folds and between the true and false vocal folds of this adult Bonobo specimen. There are cilia on the upper part of the epithelium where there is little or no contact between the vocal folds and the false vocal folds (Figure 1). This is visible in the ventricular part in Figure 2. This last point is important since this could help to understand acoustic observations made during Bonobo vocalizations. This is particularly true for the contribution of the false vocal folds and the air sacs which contribute to their acoustic signature. This needs confirmation with data from other specimens but suggests however that a comparison of the histological structure of vocal folds between humans and Bonobo may shed light on differences in their vocalizations.