A patient presents to the emergency depament complaining of fever, chills, and a painful mass adjacent to his anus. On examination, a tender, fluctuant mass is palpated. Purulent material is noted through the skin and the diagnosis of ischioanal abscess is made. The patient is taken to the operating room, and incision and drainage of the abscess is performed. During the procedure, the extent of the lesion is underestimated, and the inferior rectal nerve is damaged. This nerve is a direct branch of which of the following nerves?