Vibrissae Structure in the Rhesus Monkey

Most mammals and all primates, except man, develop vibrissae on the face. Histologically, the sinus hairs around the mouth and across the brow ridges of rhesus monkeys resemble those of nonprimate mammals except for their smaller size and follicles lack of skeletal muscle attachments. These follicles grow in especially great density along the glabrous borders of the mouth. Unlike the linearly arranged vibrissae on the muzzles of more primitive mammals, the sinus hairs of the rhesus monkeys are distributed in less clearly defined patterns around the facial disc. Studies of vibrissae in nonprimate species indicate that these sensory hairs function in relation to eye- blinking, orienting, and biting reflexes, or in conjunction with olfaction.