NERVOUS TISSUES AND SYSTEMS. 85 



BRAIN. 



The brain comprises the medulla oblongata, the cerebellum, and 

 the cerebrum. It is directly connected with the spinal cord, and, 

 thus, with the nerve structures of all parts of the body. It sends 

 forth twelve pairs of cranial nerves, which supply the organs of 

 sense, lungs, heart, etc. It possesses two kinds of nervous mat- 

 ter, gray and white. The arrangement of these substances is the re- 

 verse of that exhibited in the spinal cord, except that in the me- 

 dulla oblongata the gray matter is centrally located. The gray mat- 

 ter is found in the cerebral cortex, the corpora striata, optic thai ami, 

 corpora quadrigemina, cerebral ganglia, the lining of the ventrielos, 

 and the cerebellar cortex. 



The whole brain is encased with three characteristic membranes, 

 the dura mater on the outside, next to this the arachnoid membrane, 

 and on the inside, immediately investing the brain, the pia mater. 



The dura mater is a dense, elastic, fibrous membrane. It sends 

 three processes into the brain for its protection and support, and also 

 penetrates the skull. The arachnoid membrane lies between the 

 dura and pia, and is extremely thin and delicate. Between the 

 arachnoid and pia is a space filled with the cerebro-spinal fluid. The 

 membrane is composed of white fibres and elastic tissue. The pia 

 mater consists of a plexus of blood vessels held together by delicate 

 areolar tissue. 



OUTLINE OF THE BRAIN. 



Medulla ob- 

 longata 



Anterior median. 

 Fissures. . . . \ Posterior median. 



Two lateral fissures. 



Anterior. 

 Surfaces ..A Lateral. 



Posterior. 

 f White matter. 



Substances. { 



[_ Gray matter. 



f Cerebellar f Molecular layer. 



n , ,, cortex . . . < Layer of Purkinji's cells. 



Cerebellum . . j | Granular layer. 



I Medulla, or 



white mat- f Medullated fibres, 

 ter. 



Connective tissue. 



