The afferent connections of the magnocellular preoptic (poma), lateral preoptic (pol), and medial preoptic (pom)nuclei have been investigated with horseradish peroxidase (HRP) method in the rat. Our findings indicated that1. poma mainly receives projection from the rhinencephalic structures including the anterior olfactory nucleus, olfactory tubercle, piriform cortex, entorhinal cortex, the nucleus of lateral olfactory tract, the anterior amygdaloid area, and the cortical amygdaloid nucleus;2. pom mainly receives afferent fibers from some of the medial hypothalamic nuclei;3. pol has the most extensive fiber input, mainly from some of the brain stem nuclei; and4. poma is the only one of the preoptic nuclei which has reciprocal connections with the contralateral forebrain structrues. It is interesting that the poma and pol receive the afferent fibers from different prefrontal cortical regions and the dorsal portion of pom may have input from the lateral reticular nucleus and nucleus tractus solitarii that the ventral portion may not have.In addition, a large number of HRP-labeled cells could be seen in the supraoptic nucleus after injecting any one of the preoptic nuclei and the possible signification was discussed.

The rami communicantes in five adult cadavers were examined.All the rami were taken down serially in three cadavers;each pair was cut transversely into two parts to be separately sectioned and treated by the Weigert-Pal and Ranson's pyridine silver methods.Their components were observed under microscope for the presence or absence of the myelin sheath in order to identify a filament as of white or gray ramus. On the thoraco-lumbar levels,the shallower or lower ramus was coarser of the pair and its junction with the respective spinal nerve was also farther from the corresponding intervertebral foramen.It was composed mainly of myelinated fibers and hence designated as the white ramus.On the other hand,the deeper or upper member of the two was relatively slender and its junction with the pertinent spinal nerve was nearer to the foramen.This branch contained chiefly unmyelinated fibers and represented the gray ramus.The oblique ramus,which occurred occasionally and consisted mainly of myelinated elements,was also clas- sified with the white ramus. The White rami were definitely distributed from thoracic 1 to lumbar 3.The gray rami of the cervical 6-8 and lumbar 4-5 also contained a number of mye- linated fibers and even some sympathetic cells were aberrated into them.The upper cervical and lower sacral gray rami contained but rarely any myelinated elements. Thus,the white and gray communicating rami were formed not purely of myelinated or unmyelinated fibers,but a mixture of both,with,however,the predominence of one kind.In general,it is possible to ascertain the relative positions of the two rami in a cadaver under dissection.