Fig. 4. Sagittal view of the trajectory of a single olivocerebellar axon innervating vermal lobule VI and VII and hemispheric crus I in an irradiated rat, reconstructed from 72 serial sagittal sections. Inset shows the nearly complete path of this axon from the ventral medulla near the injection site. This axon was labeled presumably by the uptake of BDA at the portion passing through the injection site (the right inferior olive). Because the number of labeled axons was small in the right cerebellar cortex, tracing all thin collaterals was possible. Black arrowheads indicate climbing fiber terminal arborizations, andopen arrowheads indicate non-climbing fiber thin collaterals. Abbreviations in this and subsequent figures:I-X, lobules I-X; a-d, sublobules a-d;C, caudal; CN, cerebellar nucleus;CP, copula pyramidis; Crus I, crus I ansiform lobule; Crus II, crus II ansiform lobule;D, dorsal; DPFL, dorsal paraflocculus;FL, flocculus; GL, granular layer;ICP, inferior cerebellar peduncle; IO, inferior olive; ML, molecular layer;Param, paramedian lobule; PCL, Purkinje cell layer; R, rostral; Sim, simple lobule; V, ventral; VPFL, ventral paraflocculus; WM, white matter.