154 THE NERVOUS SYSTEM. 



white, central portion, gives the latter a some what branched 

 appearance. This peculiar appearance lias been called 



FIG. 42. VERTICAL SECTION OF THE BRAIN. 



A, Left Hemisphere of Cerebrum. D, The Pons Varolii. 



B, Corpus Callosum. E, Upper extremity of the Spinal Cora, 



C, Optic Thalamup. F, The Arbor Vitae. 



the arbor vitce, or the " tree of life," from the fact that 

 when a section of the organ is made, it bears some resem- 

 blance to the trunk and branches of a tree (Fig. 42, F). 

 In size, this cerebellum, or "little brain," is less than one- 

 eighth of the cerebrum. 



11. From the under surface of the cerebrum, and from 

 the front margin of the cerebellum, fibres collect together 

 to form the medulla oUongata (Fig. 43, MA), which, on is- 

 suing from the skull, enters the spinal column, and then 

 becomes known as the spinal cord. From the base of the 

 brain, and from the sides of the medulla originate, also, 

 the cranial nerves, of which there are twelve pairs. These 

 nerves are round cords of glistening white appearance, and, 



4 



11. Medulla oblongata? Cranial nerves? Their shape and position ? 



