Lewis & Short

sĭāgŏnes, um, m., = σιαγόνες, the muscles which support the jaw, the maxillary muscles; acc. siagonas, Cael. Aur. Tard. 1, 1, 37; 1, 4, 90.
Called also sĭāgŏnītae, ārum, m., = σιαγονῖται, Cael. Aur. Acut. 2, 10, 59; 2, 3, 6; 2, 3, 8.