604 



THE NERVOUS SYSTEM 



In reptiles and birds the cerebral ganglia attain a still further development 

 and in Mammalia the cerebral hemispheres exceed in weight all the rest of the 

 brain. As we ascend the scale, the relative size of the cerebrum increases, till 



EL v 



FlG. 373. Longitudinal and Vertical Diagrammatic Section of a Vertebrate Brain. 

 Letters as before. Lamina terminalis is represented by the strong black line joining Pn 

 and Py. (Huxley.) 



FIG. 374. Base of the Brain, i, Superior longitudinal fissure; 2, 2', 2", anterior 

 cerebral lobe; 3, fissure of Sylvius, between anterior and 4, 4', 4", middle cerebral lobe; 

 5 5' posterior lobe; 6, medulla oblongata. The figure is in the right anterior pyramid; 7, 

 8, 9, 10, the cerebellum; +, the inferior vermiform process. The figures from 7. to IX. 

 are placed against the corresponding cerebral nerves; 777. is placed on the right cms cerebri. 

 VI. and F77. on the pons Varolii; X., the first cervical or suboccipital nerve. 



Thomson.) X 



(Allen 



in the higher apes and man the hemispheres, which commenced as two little 

 lateral buds from the anterior cerebral vesicle, having grown upward and 

 backward, completely covering in and hiding from view practically all the 



