The fairly thin tongue of the dog is used mainly for guiding food to the throat, for licking the coat clean, and for perspiration. When a dog is overheated, it cools off by hanging its tongue out and panting. As it pants, the evaporation of perspiration from its tongue cools the animal. A dog's ears either stick up or hang down. The earliest dogs probably had erect ears, but the ears began to droop in smaller, later breeds because of excessive ear skin.
Dogs have a fine sense of hearing.
They can hear sounds at frequencies too high for people to hear. Each eye of a dog has three eyelids, the main upper and lower lids and a third lid hidden between them in the inner corner of the eye. The third eyelid can sweep across the transparent cornea of the eye and clean it like a windshield wiper. The head and body of a dog are connected by its neck. The neck may be long or short, depending on the size of the seven bones that support it.