CHAPTER VII 



THE NERVOUS SYSTEM 



nervous system is concerned chiefly with the func- 

 tions of sensation, motion, and volition. It is through this 

 system that all actions, voluntary and involuntary, are 

 controlled. It is made up of the cerebrospinal center, and 

 the numerous slender or thread-like prolongations that 

 emanate from the center, called nerves, and which are 

 distributed to every tissue and part of the body, excepting 

 the extremities of the nails, the hair, and adipose tissue. 

 The substance of the brain, spinal cord, and nerves is very 

 similar. It is of soft or pulpy consistence, and of a whit- 

 ish or cineritious color. 



The Brain. The brain in the human subject is large, 

 and, with its membranes and vessels, occupies the cavity 

 of the skull. It consists of three portions the cerebrum, 

 or anterior and larger portion, the cerebellum, which is 

 about one-seventh the size of the cerebrum, and is situ- 

 ated in the back and lower portion of the skull, and the 

 medulla oblongata, situated below the cerebellum. The 

 brain is entirely surrounded by membranes the dura 

 mater, the arachnoid, and the pia mater. 



The dura mater is a firm membrane, which lines the cra- 

 nial cavity and acting as the periosteum of the cranial 

 bones. It forms septa the falx cerebri, the falx cerebelli, 

 and the tentorium which form partitions between the 

 different parts of the brain. 



The arachnoid is a serous membrane that invests the 

 brain and spinal cord. Like other serous membranes, it is 

 a closed sac. 



198 



