In the development of a neuroblast the push of "the cone of growth" at the end of the axone must be equaled by the resistance offered to the opposite side of the neuroblast. Conditions being equal, the advance of "the cone of growth" and the retreat of the cell-body are inversely pro portional to the area of the pushing surfaces. Because of this simple fact, the bodies of the nuclear neurones tend to recede from the ventricle as their axones push toward it; but, being resisted by the axonic push of the cor tical neurones, they remain close to the ventricle and constitute the dentate, emboliform, globose and fastigial nuclei. The nuclear cells form fixed points of resistance for the intrinsic cortical neurones; hence, as their axones grow, their bodies are pushed out into the marginal layer, where they take up their adult positions and develop into the wonderful cells of Purkinje.
The stellate and granule cells of the cerebellar cortex are all immigrants. They migrate from the sensory column of the medulla, located in the lip of the rhomboid fossa (fourth ventricle). In the latter part of the second month this migration begins; it continues to flow steadily until the super ficial part of the marginal layer is crowded with cells. It appears to be a
passive migration, the cells being carried into the cerebellum by the in growing tracts from the pons and spinal cord. In the marginal layer a large number of the immigrant cells complete their life histories, throwing out their axones and dendrites and establishing relations with one another, with the corticipetal axones and with the cells of Purkinje; but a consider able number of small neuroblasts, whose axones are directed toward the surface, leave this superficial position. Their axones branch T-like, diverging parallel with the edge of the gyri; and, with the growth of the axones, the cell-bodies gradually sink down between the Purkinje cells into the mantle layer. Such centripetal migration continues until a dense layer of small cell-bodies is formed subjacent to the cells of Purkinje. The cell bodies possess so little cytoplasm the layer looks like a collection of nuclei or granules, hence, the name, granular layer. Each granule cell gives off four to eight dendrites that end in the form of claw-like tufts; they estab lish synapses with one another, with the large second type cells of the granular layer and with some of the corticipetal fibers.