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A MANUAL OF ANA TO MY. 



covers in the rest of the brain. From the anterior inferior 

 part of the forebrain extends forward a narrow prolonga- 

 tion, whose cavity is at first in direct communication with 

 the cavity of the forebrain. This prolongation is the 

 olfactory lobe. Its cavity becomes filled up during develop- 

 ment and is no longer found in the adult. From the floor 



Diag. 15. A Fourth Stage in the Development of the Brain. VERTICAL 

 ANTEROPOSTERIOR SECTION AT ONE SIDE OF THE MEDIAN LINE. (Modified from 

 Edinger.) i, Olfactory bulb, central cavity obliterated. 2, Forebrain. (Cerebrum.) 

 3, Attenuated roof of midbrain involuted into the cavity of the cerebral vesicles in 

 front of the velum interpositum. 4, Pineal gland. 5, Corpora quadrigemina. 6, 

 Cerebellum. 7, Attenuated roof of afterbrain which becomes involuted into the cavity 

 of the fourth ventricle in front of its choroid plexus. 8, Corpus striatum. The figure 

 is placed on the fibres of the internal capsule which are beginning to be developed. 

 9, Optic thalamus. 10, Crus cerebri. n, Pons. 12, Medulla, a, Lateral ventricle. 6, 

 Third ventricle, c, Aqueduct of Sylvius, d. Fourth ventricle. <?, Central canal of 

 spinal cord, f, Caudate, and g, Lenticular nuclei of the corpus striatum beginning to 

 appear, h, Transverse fibres of pons developing. 



of the vesicles opposite to and behind the site of the foramen 

 of Monro there takes place an upgrowth of cells, in two 

 elongated masses, which overlap each other. The long 



