The primate hyolaryngeal apparatus and herbivorous modifications

The predominantly herbivorous diet of the howler and baboon is responsible for modification in the configuration of the hyolaryngeal apparatus. In a herbivorous primate the air sac located in the concavity of the body of the hyoid bone takes on a resonating function. There is definite correlation between : (1) the presence of a large epiglottis with a convex superior surface, (2) close apposition of the soft palate with the epiglottis, (3) presence of high aryepiglottic and lateral epiglottic folds, (4) presence of air sacs and (5) concavity of the posterior surface of the body of the hyoid bone (basihyal), and the herbivorous diet of the species. These characteristics are not as pronounced in the less herbivorous rhesus, even less so in the frugivorous capuchin and the least in the insectivorous marmoset.