736. The CEREBELLUM is about seven times smaller than the cerebrum. Like that organ, it is composed of white and gray matter, but the gray constitutes the larger portion. Its surface is formed of parallel plates separated by fissures. The white matter is so arranged, that when cut vertically, the appearance of the trunk and branches of a tree (_ar´bor vi´tæ_) is presented. It is situated under the posterior lobe of the cerebrum, from which it is separated by a process of the dura mater, called the _ten-to´ri-um_. -=-=-=-=-=-=-=-=-=-=-=-= 733. Describe the appearance of the brain when a horizontal section has been made. What is the gray border often called? What connects the hemispheres? 734. Describe the ventricles of the brain. In the disease called "dropsy of the brain," where is the water deposited? 735. What is the character of the brain in childhood? In adults? 736. How does the cerebellum compare in size with the cerebrum? -=-=-=-=-=-=-=-=-=-=-=-= [Illustration: Fig. 122. The under surface, or base, of the brain and origin of the cranial nerves. 1, 1, The anterior lobes of the cerebrum. 2, 2, The middle lobes. 3, 3, The posterior lobes, almost concealed by the cerebellum. 4, 4, The cerebellum. 7, 7, The longitudinal fissure that divides the brain into two hemispheres. 8, The first pair of nerves. 9, 9, The second pair of nerves. 10, The decussation, or crossing, of its fibres. 13, 13, The third pair of nerves. 14, The pons varolii. 15, 15, The fourth pair of nerves. 16, 16, The fifth pair of nerves. 17, The sixth pair of nerves. 18, 18, The seventh and eighth pair of nerves. 19, The medulla oblongata, with the crossing of some of its fibres exhibited. 20, The ninth pair of nerves. 21, The tenth pair of nerves, 22, The eleventh pair of nerves. 23, The twelfth pair of nerves.] -=-=-=-=-=-=-=-=-=-=-=-= Describe this portion of the brain. Explain fig. 122. -=-=-=-=-=-=-=-=-=-=-=-= 737. The MEDULLA OBLONGATA, or that portion of the spinal cord which is within the skull, consists of three pairs of bodies, (_cor´pus py-ram-i-da´le_, _res-ti-for´me_, and _ol-i-va´re_,) united in a single bulb.