17 young healthy rabbits weighing from 520 to 720 gins,ageing 38～48 postnatal days,were used for this study.Seven to fourteen days following spinal lesions at diffe- rent levels the animals were killed and serial transverse sections of thc brain stem were stained with thionin,the retrograde cell degenerations within the red nucleus were studied. An analysis of the chromatolysis indicates that the rubrospinal fibers are largely crossed and a few fibers to the cervical cord are uncrossed.Furthermore,a somatotopical localization exists within the contralateral red nucleus with respect to the rubrospinal tract,i.e.the cervical projections of the fibers system take origin from the dorsal part of the red nucleus almost throughout its whole extent,the thoracic projections from the ventral part of the caudal five-sixths of the red nucleus,and the lumbar projections from the centro-ventral part of the caudal third of the nucleus. It also indicates that all types of cells in the red nucleus,not only the large ones, give rise to the rubrospinal tract.The spinal porjections of this fiber tract may descend as far as the lumbar cord.

Nine adult healthy rabbits were used in this study.In these animals attemptswere made to produce lesions in different parts of the cerebellar hemispheres.Largelesions of the left cerebellar hemisphere were produced by an aspiration technique.Small lesions of the cerebellar cortex or of the dentate nucleus were produced bystereotaxic electrolysis.All animals were sacrificed 3～7 days after the operation.The brains were cut at 25～30 ? in serial transverse sections on freezing microtome.The sections were stained with Fink-Heimer method.The degenerating fibers and terminals are found in the bilateral nuclei of Ⅲ,Ⅳ and Ⅵ cranial nerves The degenerations are predominant in the contralateraloculomotor nucleus but less in the ipsilateral side.On the contrary,it is slightlydominant in the ipsilateral trochlear and abducens nuclei,but less in the contrala-teral ones.It is shown that these fibers arise from the dentate nucleus.The functional significance of this fibers system is discussed.

Twenty five adult healthy rabbits were used in this study. They were divided into three experimental groups. In the first group, the great part of the left eerebellar hemisphere including the dentate nucleus was sucked out, a stereotaxic lesion of the left dentate nucleus was made, or a small part of the cerebellar cortex of hemisphere was destroyed. In the second group, the great part of the vermis was aspirated, the left fastigial nucleus or the vermal cortex was damaged with the stereotaxie electrolysis. In the third group, the left paraflocculus was sucked out. The animals survived for 3～8 days. The serial frozen transverse sections of the brain stem together with the cerebellum were cut at 25～30 ?m and stained with the Fink-Heimer method. The degenerating fibers in sections were traced under light microscope.The results are as follows:1. The first group: The degenerating fibers from the left dentate nucleus enter into the ipsilateral brachium conjunctivum, some of them emerge from the medial side of the brachium eonjunetivum, then proceed forward and pass through the trigeminal mesencephalie nucleus and end into the ipsilateral nucleus eaeruleus and subcaeruleus. But no degenerating fibers within nucleus caeruleus are observed if a lesion only injured the cerebellar cortex of hemisphere.2. The second group: Except the projection to the cerebellar central nuclei and other regions of the brain stem, some degenerating fibers arising from the vermis (including vermal cortex and fastigial nucleus) ascend up into bilateral nucleus parabrachialis and a few of them enter into the ventral part of the brachium conjunctivum. These degenerating fibers continue forward to the rostral end of the pons and pass through the trigeminal mesencephalic nucleus to terminate in locus caeru leus and subcaeruleus.3. The third group: A few degenerating fibers from the paraflocculus terminate in the locus caeruleus.The functional significance of the cerebellocaeruleus projection was discussed.