278 



MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



spect to the development of the hemisphere itself, by which a separation of the 

 same into different divisions very decidedly and distinctly appears. 



Huschke 1 also doubts that the brain has adapted itself to the skull, but holds 

 rather that the reverse is the case. 



The third and last view is merely a combination of the other two. According 

 to this, certain of the fissures and convolutions, including the most important, are 

 produced by merely mechanical causes, whilst others owe their origin to morpho- 

 logical processes of growth in the brain substance itself, the fissures representing 

 lines of retarded, whilst the convolutions represent areas of increased growth. 



The last is the view adopted by the writer. 



DEVELOPMENT OF THE BRAIN. 



The brain arises from the primitive medullary tube, first by the expansion 

 of its anterior end into three so-called cerebral vesicles known as the primary 

 cerebral vesicles. From the most anterior of these, which eventually forms the 

 cavity of the third ventricle of the brain with its surrounding parts, known as 

 the thalamencephalon, there are given off anteriorly a pair of secondary vesicles, 

 known as the right and left cerebral vesicles, and these give rise respectively 

 to the right and left hemispheres, the contained cavities becoming the corres- 

 ponding right and left ventricles, which communicate posteriorly with the third 



ventricle by means of a common Y shaped opening, 

 the foramen of Munroe, as shown in fig. 1. It will 

 be seen that the two hemispheres at this stage of 

 evolution consist of two ovoidal sacs connected with 

 the thalamencephalon posteriorly, whilst anteriorly 

 they each give off in their turn a vesicle which 

 becomes the olfactory bulb. As development pro- 

 ceeds there arise in connection with these sacs all 

 the important structures of the adult brain. A por- 

 tion of the internal walls on each side forms the 

 corpora striata, whilst the remaining portion devel- 

 ops the cerebral mass, the outer or peripheric wall 

 differentiating into the cortical surface, producing 

 the covering of gray ganglionic material which 

 forms the substance of the cerebral convolutions. 

 The 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 around 

 the cerebral peduncle to form the anterior or frontal portion, whilst the postero- 

 inferior curves downward and forward underneath the cerebral peduncle to form 

 the inferior or temporal portion of the hemisphere. In this way is produced the 



Opt. Bud 

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1 Schiidel, Him, etc' 



