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HANDBOOK OF PHYSIOLOGY. 



est of the three, is bent downwards, and the middle one comes to oc- 

 cupy the highest position. (2.) A sharp bend, with the convexity for- 

 wards, which runs in from behind beneath the rudimentary cerebellum 

 separating it from the medulla. 



Thus, five fundamental parts of the foetal brain may be distinguished, 



FIG. 483. Early stages n development of human brain (magnified). 1, 2, 3, are from an em- 

 bryo about seven weeks old; 4, about three months old; m, middle cerebral vesicle (mesencepha- 

 Jon); c, cerebellum ; mo, medulla oblongata;*, thalamencephalon; h, hemispheres; i', infundibulum; 

 Fig. 3 shows the several curves which occur in the course of development; Fig. 4 is a lateral view, 

 showing the great enlargement of the cerebral hemispheres which have covered in the thalami, 

 leaving the optic lobes, m, uncovered. (Koliker.) 



N.B. In Fig. 2 the line i terminates in the right hemisphere; it ought to be continued into the 

 thalamencephalon. 



which, together with the parts developed from them, may be presented 

 in the following tabular view: 



Table of Parts Developed from Fundamental Parts of Brain. 



I. Anterior 

 Primary 

 Vesicle. 



II. Middle 

 Primary 

 Vesicle. 



1. Prosencephalon. 



2. Thalamencephalon 

 (Diencephalon). 



3. Mesencephalon. 



Cerebral hemispheres, cor- 

 pora striata, corpus callo- 

 sum, fornix, lateral ven- 

 tricles, olfactory bulb. 



f Thalami optici, pineal 

 gland (part of), pituitary 



<( body, third ventricle, op- 

 tic nerve (primarily), in- 



[_ fundibulum. 



f Corpora quadrigemina, cru- 



J ra cerebri, aqueduct of 



1 Sylvius, optic nerve (sec- 



[ ondarily). 



