The angioarchitectonic regions in the medulla oblongata and the midbrain of 14 grown-up guinea pigs are discribed. According to direction and number of the supplying arteries, three sections are distinguished. The medial part is supplied worst. It contains the medial row of the nuclei of the cranial nerves. The more lateral parts have always double or treble supplies. They are distinguished by a high capillary density. Those parts are associated with the medullar nuclei of the cranial nerves.