Tegmentum(Latin) = quilt, "roof".
The tegmentary part of the brainstem contains cranial nerve nuclei, various level-specific nuclei, conduction pathways and formatio reticularis.
In the mesencephalon, the tegmentum forms the portion of tissue located between the lamina tecti and the crura cerebri.
In pons, the tegmentum is the tissue portion located between 4.de ventricle and the "pons lump", i.e. the part of the pons that contains the pons nuclei, the corticopontina pathways, the pontocerebellar pathways and the pyramidal pathway.
In the medulla oblongata, the concept of "tegmentum" becomes more or less superfluous. If used, it should refer to the tissue portion that lies dorsally about/behind the pyramids.