Evolution of the Maxillary Canal (IMAGE) University of the Witwatersrand Caption The evolution of the maxillary canal for the trigeminal nerve (in green) in Therapsida. Abbreviations (Ma millions of year) (Prb Probainognathia clade) (Thr Therapsida clade). Credit Wits University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.