Abstract
1. The mamillothalamic tract arises from all of the mamillary nuclei. The pars medialis of the medial mamillary nucleus sends fibers ipsilaterally to the pars magnocellularis of the anteroventral nucleus and the anteromedial nucleus of the thalamus. Its medial portion projects to the medial portion of the pars magnocellularis of the anteroventral nucleus and the dorsomedial part of the anteromedial nucleus, while the lateral portion projects to the dorsolateral portion of the pars magnocellularis of the anteroventral nucleus. The pars lateralis of the medial mamillary nucleus sends fibers to the pars parvocellularis of the anteroventral nucleus of the same side and also to the anterodorsal nucleus of both sides. The lateral mamillary nucleus is connected with both anterodorsal nuclei.
2. The mamillary nuclei contribute fibers to the medial forebrain bundle, projecting to the medial septal nucleus. Some of these mamilloseptal fibers end in the lateral hypothalamic and the lateral preoptic nuclei on their way to the septal nucleus.
3. The mamilldtegmental tract divides into the main dorsal and the ventral bundles. Although the latter is directed ventrally to the nucleus reticularis tegmenti pontis and the pontine nuclei, the former passes dorsally to the dorsal and ventral tegmental nuclei, and the central gray of the pons. The fibers from the pars medialis of the medial mamillary nucleus end chiefly in the ventral tegmental nucleus, particularly the small-celled part, but some of them run further dorsally to enter the large-celled ventral part of the dorsal tegmental nucleus. It should be mentioned that a few fibers from the pars medialis of the medial mamillary nucleus partly run dorsally along the median raphe to enter the central gray of the pons, and partly cross the midline to end in the ventral tegmental nucleus of the opposite side, though a very few fibers pass through this nucleus. The fibers from the pars lateralis of the medial mamillary nucleus are directed largely to the dorsal tegmental nucleus, particularly its large-celled ventral part, and partly to the ventral tegmental nucleus. Within the dorsal nucleus most fibers terminate, but some pass through it to end in the central gray of the pons. On the other hand, a few fibers from the pars lateralis of the medial mamillary nucleus run dorsally along the median raphe to terminate in the central gray of the pons, without entering the tegmental nuclei. The fibers from the lateral mamillary nucleus are distributed to the ventral and dorsal tegmental nuclei, and to the central gray of the pans along the median raphe. Besides, they are distributed to the reticular formation and the tegmental laterodorsal nucleus.
4. A small number of fibers from the mamillary nuclei descend in the mamillary peduncle and can be traced to the middle levels of the interpeduncular nucleus. During their course many of them spread dorsally to join the mamillotegmental fibers.
5. The mamillary body contributes fibers to the dorsal longitudinal fasciculus of Schütz. These fibers descend in the mesencephalie central gray of the same side as far caudally as the lowest level of the superior colliculus, spreading out laterally into the reticular formation throughout their course.
