The purpose of the present investigation is to clarify the shapes of thehuman pterygoid plexus. For the purpose of this study, Fukuoka Dental Collegeobtained 71 tissue blocks containing pterygoid plexus from 37 Japanese cadaversbetween the ages of 30-90years. The blocks were sectioned at 5mm by EXAKT [○!R]cutting system using a diamondband saw (200μm in thickness), and then were observed both macro andmicroscopically under a dissecting microscope. The tissue sections obtainedfrom some tissue blocks were stained histologically and observedmicroscopically. Cranial blocks were also observed, using an MRI, andafterwards compared with those of living human specimens. The results were asfollows. 1. The pterygoid plexus, which followed from an ovale plexus, waslocated inside the lateral pterygoid muscle from the top of the infratemporalfossa, to the bottom line of the middle lateral pterygoid muscle. 2. Theconstituent veins of the pterygoid plexus presented a sinus like structure witheither thick or thin trabeculae. 3. The plexus parts and the sinus venosusparts of the pterygoid plexus were also confirmed by the MRI. 4. Theconstituent veins of the pterygoid plexus could be classified as type I, whichpresented a sinus like structure 3 mm in diameter, and type II, which presenteda sinus like structure 3 mm and over. The frequency in appearance of both typeI and II was 39.4% and 60.6% respectively. 5. In the constituent blood vesselsof the pterygoid plexus, venous valve and artriovenous anastomoses, wereobserved. In conclusion, these findings suggest that the pterygoid plexus has ablood storable shape which easily causes a stagnant blood stream followed by adisturbance in the function of temporomandibular joints and the fatigue ofmasticatory muscle groups. This circulatory disturbance ultimatily appears tohave an influence on the whole masticatory system.