. A laboratory manual and text-book of embryology. Embryology. 334 THE MORPHOGENESIS OF THE CENTRAL NERVOUS SYSTEM cross to the opposite side and form the brachium pontis of the cerebellum. Cere- bral fibers from the cerebral peduncles end about the cells of the pontine nuclei. Others pass through the pons as fascicles of the pyramidal tracts. Cerebellum.—When the alar plates of the cranial end of the myelencephalon are bent out laterally the caudal portions of their continuations into the meten- cephalic region are carried laterally also. As a result, the alar plate of the meten- cephalon tak
. A laboratory manual and text-book of embryology. Embryology. 334 THE MORPHOGENESIS OF THE CENTRAL NERVOUS SYSTEM cross to the opposite side and form the brachium pontis of the cerebellum. Cere- bral fibers from the cerebral peduncles end about the cells of the pontine nuclei. Others pass through the pons as fascicles of the pyramidal tracts. Cerebellum.—When the alar plates of the cranial end of the myelencephalon are bent out laterally the caudal portions of their continuations into the meten- cephalic region are carried laterally also. As a result, the alar plate of the meten- cephalon takes up a transverse JVleseh cephalon Cerebellum Ependymal layer. B Mesencephalon Cerebellum position and forms the anlages of the cerebellum (Fig. 319 A). During the second month the paired cerebellar plates thicken and bulge into the ventricle (Fig. 320 A). Near the mid- line a thickening indicates the anlage of the vermis, while the remainder of the alar plates form the anlages of the lateral lobes or cerebellar hemispheres. The cerebellar anlages grow rapidly laterally and also in length so that their surfaces are folded transversely. During the third month their walls bulge outward and form on either side a convex lateral lobe connected with the pons by the brachium pontis (Fig. 319 C). In the meantime, the anlages of the vermis have fused in the mid- line producing a single structure marked by transverse fissures. The rhombic lip gives rise to the flocculus and nodulus. Between the third and fifth months the cortex cerebelli grows more rapidly than the deeper layers of the cerebellum and its principal lobes, folds and fissures are formed (Fig. 319 C, D). The hemispheres derived from the lateral lobes are the last to be differentiated. Their fissures do not appear until the fifth month. Cranial to the cerebellum the wall of the neural tube remains thin dorsally. Please note that these images are extracted from scanned page images that may have been digitally enhanced for r
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