CORPUS-CALLOSUM DEVELOPMENT

Corpus callosum embryology can be divided into three parts: during ''c ommissuration'', a cellular mass develops between two telencephalic ve sicles. The primitive lamina terminalis corresponds to the closing poi nt of the anterior neuropore. Its dorsal part grows and forms the lami na reuniens (6-8 intra uterine weeks, IUW). From ventral to dorsal, th is lamina reuniens gives rise to the area praecommissuralis (origin of the anterior commissure), to the primordium hippocampi (10 I.U.W., fo rnix), and to the massa commissuralis (10 S.I.U., corpus callosum). Fi bers arising from the developing hemispheres run through this primitiv e corpus callosum. The growth of the corpus callosum follows the expan sion of the hemispheres, in a rostro-caudal and then dorso-ventral cir cular movement. The last part of the corpus callosum to form is the ro strum. Maturation occurs postnatally, and corresponds to axomal elimin ation, and myelination, progressively changing the callosal connection pattern of the newborn and infant into the adult pattern.