Dante invokes the Muses of the lowest and hardest poetry: this description requires a roughness that ordinary style cannot provide. The frozen lake of Cocytus is divided into regions. Caina — named for Cain — holds the traitors to kin, frozen to their necks, faces down in the ice, teeth chattering, tears freezing in their eye sockets. Dante nearly steps on a head; it curses him. Two brothers — Napoleone and Alessandro degli Alberti, who killed each other over their inheritance — are frozen face to face. Mordred, Focaccia, Sassol Mascheroni, Camicion de' Pazzi are here.
Antenora — named for the Trojan Antenor who betrayed Troy to the Greeks — holds the traitors to their homeland or political party. Moving through, Dante kicks a face in the ice. The shade curses. Dante grabs its hair and pulls, demanding its name — threatening to leave it bald. It refuses. Another shade tells Dante the name: Bocca degli Abati, a Florentine who, at the Battle of Montaperti, cut off the standard-bearer's hand at a crucial moment, routing the Guelphs. His infamy is complete even here.
Then Dante sees something extraordinary: one sinner gnawing the skull of another from behind, his teeth working into the bone where the neck meets the head, like bread. He stops and watches. The gnawer lifts his bloody mouth and speaks: he is Count Ugolino della Gherardesca of Pisa; the skull he gnaws is Archbishop Ruggieri, who imprisoned Ugolino and his sons in a tower and starved them to death. The account of what followed will be given in the next canto.