The maxilla consists of maxillary bones that form the upper jaw; together they are the keystone of the face, for all other immovable facial bones are connected to them. Portions of these bones make up the front of the roof of the mouth (hard palate), the floors of the orbits, and the sides and floor of the nasal cavity. They also contain the sockets of the upper teeth. Inside the maxillae, on the sides the nasal cavity, are the maxillary sinuses (antrum of Highmore). These air-filled spaces are the largest of the sinuses, and they extend from the floor of the orbits to the roots of the upper teeth. During development, portions of the maxillary bones called palatine processes grow together and fuse along the middle to form the front section of the hard palate.