Chick embryo brains have been checked after 11, 12, 13, 14, 15, 17, 19, 21 days of incubation and 15 days after birth. Myelinization process starts at the 14th day of incubation in the medulla oblongata and extends to mesencephalon, diencephalon and telencephalon in the following days. Such a process is not simultaneous within the same vesicles, but a sequence in the myelinization of different bundles can be clearly observed. Myelinization occurs first in the long integration intersegmental ways which forward the stimulus coming from upper centers to the spinal cord. Myelinization occurring in the main bundles takes place as follows: at the 14th incubation day: medial longitudinal fasciculus, vestibulo-spinal tr.; at the 17th incubation day: dorsal and ventral arcuate systems, spino-cerebellar tr., vestibulo-cerebellar tr., lateral lemniscus, brachia conjunctiva; at the 19th incubation day: tecto-bulbar tr., tecto-thalamic tr., posterior commissure, lateral forebrain bundle; at the 15th day after birth: occipito-mesencephalic tr., cortico-septomesencephalic trs. It is possible to suppose that myelinization process takes place according to the philogenetic order as it first involves the former systems and by degrees the later ones.
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Con il contributo del Ministero per i Beni e le Attività Culturali