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554- The Brain consists of soft white, and grey nervous matter, 

 and fills the irregular cavity of the skull or cranium. It is divided 

 into four parts : — 



I. — The cerebrum, or large brain, (Plate XXXIV., A.) 

 composing about three-fourths of the whole orga'n. 



2. — The cerebellum, or small brain, (Plate XXXIV., B.J 

 situated immediately behind the cerebrum. 



3.— The pons varolii, (Plate XXXV., B. 4.) or bridge, 

 connecting the right and left portions of the cerebellum. 



4. — The medulla oblongata, (Plate XXXIV., C.J or con- 

 necting link between the spinal-cord and the brain 

 proper. 



555. The Brain is covered by three coats or membranes, called the 

 Meninges. These are (i) Dura Mater, — a tough, fibrous membrane, 

 lying in immediate contact with the bony skull ; (2) the Arachnoid 

 membrane (spider-web), or middle coat, — a very fine, delicate, 

 membrane ; and (3) the Pia Mater, which covers the surface of the 

 bram, — a very fine, extensive membrane, made up of a net-work of 

 small blood-vessels. The last-named membrane follows and covers 

 all the convolutions of the brain, and supplies it with blood. 



556. The Cerebrum, (Plate XXXV., A. 1.1. and B. 1. I.J, or large 

 brain, is divided by a fissure, into two hemispheres, each of which is 

 mapped out into numerous convolutions of grey matter, covering 

 white fibrous nerve-material. The cerebrum is said to be the main 

 seat of sensation, reason, and will. 



557. The Cerebellum, (Plate XXXV., A. 2., B. 2, 2.), or small 

 bram, has a nuddle lobe (vermis) and two lateral hemispheres, made 

 up of convolutions, that are smaller than those of the cerebrum, and 

 differently arranged. The grey nerve substance is abundant, and 

 external to the white nerve tissue. The cerebellum is thought to 

 control and regulate the voluntary muscular actions of the body. 



