450 Overall, the trajectory of the tract can be relatively easily followed; it climbs into the thalamus with a posteromedial to anterolateral direction. On sagittal sections, the main orientation of the tract is posteroventral to anterodorsal, with a 60 –65 angle with the intercommissural plane (Fig. 5). The relative stable anteroposterior position of the fct at mid-distance between the posterior commissure (pc) and midcommissural level (mcl) is recognizable in hori- zontal sections (Fig. 6). On frontal sections, the orientation is medioventral to laterodorsal, with a 40 –45 angle with the intercommissural plane (Figs. 2, 7). In myelin stain, the entrance of the ﬁbres is clearly seen in the ventral division of the ventral lateral posterior (VLpv) nucleus (Fig. 5, sagittal planes L10.8 and L11.7) with a possible extension into the ventral lateral anterior (VLa) nucleus (e.g. Figs. 4a; 5, L9 and L9.9). On its way to the VLp, most of the fct passes ventral to the subparafascicular (sPf) nucleus, anterolaterally to the parvocellular part of the ventral posterior medial (VPMpc) and VPM nuclei, and through the ventral medial nucleus (VM) at level posterior to the subthalamic nucleus and the zona incerta (ZI) (Fig. 5). It is interesting to note that at the dorsal border of the RN, a part of the fct seems to take a medial turn towards the centre me´dian nucleus (CM) (Fig. 2, section A6.0). In adjacent sections stained for AChE or immunoreacted for CaBP, the fct appears generally negative, except for Brain Struct Funct (2008) 212:443–463 PV-immunoreactivity (PV-ir), which also characterizes the RN and STh, as described below. Pallidothalamic tract The pallidothalamic tract was traced from its origin in the GPi and divided into two bundles according to previous descriptions (Vogt 1909; Vogt and Vogt 1920; Nauta and Mehler 1966): the ansa lenticularis (al) and the fasciculus lenticularis (ﬂ). The al, which represents the ventral divi- sion of the ansa lenticularis of von Monakow leaves the internal pallidum at its anteroventral edge and courses anteromedially around the posterior limb of the internal capsule (Figs. 8, 9). Its origin in the pallidum appears to extend from far rostral to near the caudal end of GPi, and from both medial and lateral subdivisions of the nucleus. From the internal capsule, the al continues posterodorsally to take a sharp descending, then an ascending turn toward the thalamus where it is joined by the ﬁbres of the ﬂ arriving over the dorsal edge of the subthalamic nucleus. The ﬂ (or ﬁeld H2 of Forel) leaves the GPi dorsal to al (Fig. 2, A21.0 and A19.0; Fig. 8, A17.5) and represents the dorsal division of the ansa lenticularis of von Monakow. Its emergence from GPi seems to extend not as far rostrally as that of al. Although the precise course of the ﬂ through the DV 0 DV 0 DV 0 mcl CeM VPMpc VM mtt VAmc CM Pf MDpc sPf RN CM VPMpc fct RN CM VPM VLpv VM fct SNr fct ft VLpv ft VM STh VLa STh L4.5 VApc al fx L7.2 al L9.9 VAmc VApc ZI fl fl ft VApc ZI Pf sPf RN CM VPLp VPM fct SNr mcl CL mtt VPMpc VM fct ft VPMpc fct ft VLpv VLa VM ft ZI fl SNr STh ft VAmc al L5.4 VApc L8.1 VApc ZIfl L10.8 R VLpv VLa STh L6.3 VAmc al L9 STh fl VM ZI fl VLpv VLa VApc Pf sPf VPMpc VM fct CM RN CM VPM fct SNc VPM fct SNr mcl VLpv ft SNr ft SNr STh STh VPLp VLpv L11.7 VApc R VLa ic ft ZIfl Fig. 5 Pallidothalamic (blue) and cerebellothalamic (orange) tracts drawn on the atlas of the human thalamus (case Hb1). The sagittal maps are arranged from medial (L4.5) to lateral (L11.7 mm) with 0.9 mm intervals. The maps are centered on the midcommissural (mcl) and intercommissural (DV0) lines. Scale bar (lower right panel): 2 mm 123