Journal of the Academy of Natural Sciences of Philadelphia . of two ovoidal sacs connected withthe thalamencephalon posteriorly, whilst anteriorlythey each give off in their turn a vesicle whichbecomes the olfactory bulb. As development pro-ceeds there arise in connection with these sacs allthe important structures of the adult brain. A por-tion of the internal walls on each side forms thecorpora striata, whilst the remaining portion devel-ops the cerebral mass, the outer or peripheric walldifferentiating into the cortical surface, producingthe covering of gray ganglionic material whichforms t
Journal of the Academy of Natural Sciences of Philadelphia . of two ovoidal sacs connected withthe thalamencephalon posteriorly, whilst anteriorlythey each give off in their turn a vesicle whichbecomes the olfactory bulb. As development pro-ceeds there arise in connection with these sacs allthe important structures of the adult brain. A por-tion of the internal walls on each side forms thecorpora striata, whilst the remaining portion devel-ops the cerebral mass, the outer or peripheric walldifferentiating into the cortical surface, producingthe covering of gray ganglionic material whichforms the substance of the cerebral cavities form the lateral ventricles, and these,following the development of the cerebral sacs, as-sume with them a crescentic form, the anterior portion of which bends aroundthe cerebral peduncle to form the anterior or frontal portion, whilst the postero-inferior curves downward and forward underneath the cerebral peduncle to formthe inferior or temporal portion of the hemisphere. In this way is produced the. Opt. Budamenceph. e Brain rebel ulla ;um 1 Schiidel, Him, etc MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 279 anterior and middle or descending horn of the lateral ventricle. This stage ofdevelopment is well represented in the figure of a three months human foetalbrain, Plate XXXV, fig. 1, where cp. is the cerebral peduncle, F the frontal. Tthe temporal and P the posterior portion of the crescentic cerebral vesicle, whilstS shows the position of the commencing fossa of Sylvius. It will also be noticedthat the mechanical action due to the surrounding cranial bones is exerting itsinfluence in moulding or pressing the hemispherical mass into shape; for whilstthe outer portion of the cerebral sacs retain their primitive rotundity, owing tothe external resistance, they have been forced together in the median line, thusproducing two opposed flat surfaces, the future mesial portions of the this way is produced the great
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