1. A foramen and a canal, referred to respectively as the masseteric foramen and masseteric canal, which occur in the mandible of many of the Diprotodontia, are described, and their incidence is recorded.
2. The foramen transmits a branch of the inferior dental artery to a specialized expansion of the deep part of the masseter in the canal.
3. This masseteric development supplements the lateral pterygoid in the production of lateral movements of the jaw; it affords also increased leverage to the mandible.
4. This condition is peculiar to, but not constantly present in, the Diprotodontia.