New Model of Human Red Nucleus Figure 12. Human magnocellular red nucleus. Photomicrographs showing the distribution of Nissl-stained mNr cells. A (11) and E (13) correspond to sections 11 and 13 in Fig. 10. C is a reversed photomicrograph of the contralateral side of A for comparison with C. The area indicated by a broken line is the outer layer of the semi-lunar shell of mNr (A, C and E). It exits between the capsule of the superior cerebellar peduncle and the parabrachial pigmented nucleus (PBP). B. High magnification views of large (L), medium (M) and small (S) neurons of the outer shell of mNr. D. Many pigmented cells exist in the parabrachial pigmented nucleus. Arrowheads indicate accumulation of pigment. E. Caudal end of vlpNr. Arrowhead indicates one giant neuron. F and G. Giant neurons among fibers of the superior cerebellar pedunculus. H. Large neuron contains pigments. Arrowhead indicates accumulation of pigment. The number in the left corner of each photomicrograph is the rostrocaudal distance (in micrometers) from the rostral tip of the red nucleus. PBP–parabrachial pigmented nucleus, vlpNr–ventorlateral part of parvicellular red nucleus. Scale bars = 100 mm in A–H. doi:10.1371/journal.pone.0006623.g012 cat, judging from the comparison between human brain materials (Nathan and Smith, 1982 [39]; Voogd, 2003 [15]) and experimental data, especially those from the chimpanzee’s brain (Strominger et al., 1985 [32]). The latter have shown that the chimpanzee’s CTT projects only to the PO. The present study with myelin stain has shown that the fine myelinated fibers vertically arise from the NB and join the medial part of the CTT (see Fig. 11D). This stands in contrast to the situation in the cat, where the NB occupies an area within the MTT (Onodera, 1984 [3]). Therefore the position of the human NB can be seen to have shifted from the ventral central gray into the reticular formation (Fig. 13C). Accordingly the zonal sheet of the human’s red nucleus might have comprised longitudinally- organized components of a well-developed vl- and dm-pNr, and an extremely well-developed NB. PLoS ONE | www.plosone.org 14 August 2009 | Volume 4 | Issue 8 | e6623