<Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> The anterior triangle is a region of the neck . </P> <P> The triangle is inverted with its apex inferior to its base which is under the chin . </P> <Table> <Tr> <Td> Inferior boundary (apex) </Td> <Td> Jugular notch in the manubrium of the sternum </Td> </Tr> <Tr> <Td> Anterior boundary </Td> <Td> Midline of the neck from chin to the jugular notch </Td> </Tr> <Tr> <Td> Posterior boundary </Td> <Td> The anterior margin of Sternocleidomastoid </Td> </Tr> <Tr> <Td> Superior boundary (base) </Td> <Td> The lower border of the body of the mandible, and a line extending from the angle of the mandible to the mastoid process </Td> </Tr> </Table>

Which of the following structures forms the roof of the anterior triangle of the neck