THE DEVELOPMENT OF THE HUMAN AUDITORY PATHWAY FROM THE COCHLEAR GANGLION TO THE MEDIAL GENICULATE BODY

Abstract

Serial transverse sections of human brains (from 4-mm. embryo to late fetal life), stained by routine methods, revealed the following facts. At 13 mm. the cochlear pathway, with dorsal nucleus of corpus trapezoideum (superior olive) and the lateral lemniscus, was clearly defined. At 19 mm. the nucleus isthmi was first seen, the tectum was developing, and the ventral tectal nucleus extended through the midbrain to the postero-lateral area of the thalamus, which becomes the medial geniculate body, and was better defined at 30 mm., in series with, and caudal to, the lateral geniculate area. At 4 cm. the inferior corpus quadrigeminum was seen, and the lateral medullary lamina demarcated the lateral thalamic nucleus (bearing the lateral and medial geniculate bodies) from the ventral thalamic nucleus. At 6-7 cm. the fibro-cellular inferior brachium was visible, and fibers of the superior brachium passed from the lateral geniculate body superficial to the medial geniculate body. By 8 cm., enlargement of the pulvinar had altered the topographic -al relationships but the 2 geniculate bodies were still demonstrably part of the lateral thalamic nuclear complex. By the 6th fetal month small multipolar neurones, surrounded by fibers, were seen in the medial geniculate body. In late fetal life enlargement of the pulvinar displaces the medial and lateral bodies still more caudally.