Introduction: The unnamed openings present in mandible are called accessory foramina. The distribution and importance of these foramina are variable, as they may serve as a conduct for nerve fibres or blood vessels. They may be important for dental surgeon and anaesthetists in performing complete nerve block and avoiding injury to the transverse get neurovascular structures. Materials & Methods: In the present study a total of 50 dry human mandibles of unknown sex and without any gross abnormality were collected from the Department of Anatomy, Saveetha Dental College, Chennai for evaluation. With the help of Vernier Calliper and Ruler, the measurements like the length, breadth and diameter of sacral hiatus will be measured. The results obtained were analysed, tabulated and represented graphically. Results: The Accessory foramina on the internal surface of the mandible was examined.Frequency of accessory mandibular foramen in 0.5mm is 40% ,in 1.0mm is 18%, in 1.5mm is 9%. Frequency of accessory mental foramen and frequency of accessory retromolar foramen in 0.25mm is 20% and 9% respectively.Conclusion: The accessory foramina transmitting during nerve block.