336 



DEVELOPMENT OF THE HUMAN BRAIN 



At a very early stage of development, believed by Tiede- 

 mann to be about the 7th week, the i^rimitive nervous 

 axis or tube undergoes a series of bendings (fig. 123, a). 



Pig. 123.— Sketches of the early form of the parts of the Cerebro-spinal Axis in 

 the Human Embryo. (Sharpc-y, after Tiedemann.) 



A, at the seventh week, hitcral view ; 1, spinal cord ; 2, medulla oblongata ; 

 8, cerebellum ; 4, mesencephalon ; 5, 6, 7, cerebrum. 



B, at the ninth week, posterior view. 1, medulla oblongata ; 2, cerebellum ; 

 8, mesciijccphalon ; 4, 5, thalami optici and cerebral hemispheres. 



C and U, lateral and posterior views of the brain of the human embryo as it 

 appears at the twelfth weeki.f intra-uterine life, a, cerebrum; b, corpora qiiadri- 

 gemina ; c, cerebellum ; d, medulla oblongata : the thalami are now covered by the 

 enlarged hemispheres, 



E, posterior view of the same brain, dissected to show the deeper parts. 1, me- 

 dulla oblongata ; 2, cerebellum ; 3, corpora quadrigemina ; 4, thalami optici ; 5, tbo 

 hemisphere turned aside; 6, the corpus striatum embedded in the hcmispheie ; 

 7, the commencement of the corpus callosum. 



F, the inner side of the right half of the same brain fcparatcd by a vertical 

 median section, showing the central or ventricular cavity. 1, 2, the spinal cord 

 and medulla oljlongata, still hollow ; 3, l)eiKl at which the pons Varolii is formed ; 

 4, cerebellum ; 5, lamina (superior cerebellar i)eduncles)4)assing up to the corpora 

 quadrigemina ; (i, crura cerebri ; 7, cori)ora qviadrigemina, still hollow ; 8, third 

 ventricle ; », infundibuliuu ; 10, thalamus, now solid ; 11. optic nerve; 12, aperture 

 leading into the lateral ventricle ; 13, commencing corpus callosum. 



The * posterior swelling ' becomes bent upon itself so 

 that its two regions (2, 3) are nearly at a right angle ; 

 while thence onwards the parts form a curve (4, 5, 6), which 

 is directed forwards and downwards. 



