The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio (pons Varolii). It is cranial to the medulla oblongata, caudal to the mid-brain, and ventral to the cerebellum. In humans and other bipeds, this means it is above the medulla, below the mid-brain, and anterior to the cerebellum. This white matter includes tracts that conduct signals from the cerebrum down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus. The pons in humans measures about 2.5 cm in length. Most of it appears as a broad anterior bulge rostral to the medulla. Posteriorly, it consists mainly of two pairs of thick stalks called cerebellar peduncles. They connect the cerebellum to the pons and mid-brain. The pons contains nuclei that relay signals from the fore-brain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture. Within the pons is the pneumotaxic center, a nucleus in the pons that regulates the change from inspiration to expiration. The pons is implicated in sleep paralysis, and also plays a role in generating dreams.