The human pharynx is conventionally divided into three sections&colon; the nasopharynx, oropharynx, and laryngopharynx. The respiratory system consists of the nose, nasopharynx, trachea, and lungs. The anterior aspect of the nasopharynx communicates through the choanae with the nasal cavities. The fluid then flows through the nasolacrimal duct and into the nasopharynx. Potential sites for this include the skin, respiratory tract, gastrointestinal tract, nasopharynx, and genitourinary tract. After the bacteria are inhaled, they initially adhere to the ciliated epithelium in the nasopharynx. In dogs a single duct connects the nasopharynx to the nasal cavity. A choana is the opening between the nasal cavity and the nasopharynx. It is located in the midline of the posterior wall of the nasopharynx. Lesions may also develop in the nasopharynx. I is a small tumor confined to nasopharynx. The nasopharynx lies directly above the throat. The back of the cavity blends, via the choanae, into the nasopharynx. It is strictly a commensal species of the nasopharynx. They also connect the nose to the throat (the nasopharynx), aiding in respiration.