After a rapid description of the pterygomandibular space, the authors describe the anatomy of the interpterygoid fasciae. The interpterygoid fasciae divide the pterygomandibular region into two compartments. The interpterygoid fascia is the most important layer; its limits are defined with precision. The individuality of the pterygotemporomaxillary fascia is less well defined. The authors then report their own study about the functional anatomy of these fasciae by means of frozen sections of color-injected fresh anatomical specimens. The results confirm the importance of the interpterygoid fasciae in guiding the anesthetic solution to the mandibular foramen in mandibular nerve block.