Paper - Development of the interfore-brain commissures in the human embryo

Development of the interfore-brain commissures in the human embryo.

By George L. Streeter. Wistar Institute of Anatomy, Philadelphia.

A morphological study of the corpus callosum and the commissure of the hippocampus, based on a series of wax-plate reconstructions of human embryos varying from 80 to 150 mm. in length. All three struc- tures cross the median line in that portion of the brain wall developed from the lamina terminalis. In 80 mm. embryos the corpus callosum consists of a round bundle of fibers lying directly on the commissure of the hippocampus, representing the condition found in non-placental animals. The succeeding growth consists in the lengthening of the fornix and caudal migration of the hippocampal commissure, the latter remaining in close relation to the caudal end of the corpus callosum, which in the meantime, by increase in number of fibers, has extended anterior to the anterior commissure and posterior so as to deck over the region of the third ventricle. The formation of a cavity in the septum lucidum occurs in embryos of about 95 mm. The anterior or olfactory division of the anterior commissure does not enter the olfactory bulb, but is traced to the cortex dorsal to the bulb.