[TA] a compact fiber bundle, comma-shaped on transverse section, composed of primary sensory fibers of the portio major of the trigeminal nerve, descending from the level of the entrance of the trigeminus in the upper pons down through the posterolateral region of the rhombencephalic tegmentum along the lateral side of the descending or spinal nucleus of the trigeminus, emerging on the posterolateral surface of the lower medulla oblongata as the trigeminal tubercle (tuberculum cinereum), and continuing as far as the second cervical segment of the spinal cord. Its fibers are distributed to the descending or spinal nucleus of the trigeminus. SYN: tractus spinalis nervi trigemini [TA], descending tract of trigeminal nerve, tractus descendens nervi trigemini.