The ultimate destination of the afferent pathways to the cerebellar cortex is a distinctive cell type called the Purkinje cell (Figure 19.8). However, the input from the cerebral cortex to the Purkinje cells is quite indirect. Neurons in the pontine nuclei receive a projection from the cerebral cortex and then relay the information to the contralateral cerebellar cortex. The axons from the pontine nuclei and other sources are called mossy fibers because of the appearance of their synaptic terminals. Mossy fibers synapse on granule cells in the granule cell layer of the cerebellar cortex (see Figures 19.8 and 19.9). The cerebellar granule cells are widely held to be the most abundant class of neurons in the human brain. They give rise to specialized axons called parallel fibers that ascend to the molecular layer of the cerebellar cortex. The parallel fibers bifurcate in the molecular layer to form T-shaped branches that relay information via excitatory synapses onto the dendritic spines of the Purkinje cells.