THE NERVOUS SYSTEM. 



The nervous elements of the cat form three systems, 

 known as the central, peripheral, and sympathetic. The 

 central nervous system includes the brain and spinal cord. 

 The peripheral system includes the twelve pairs of nerves 

 emanating from the brain and the forty pairs of nerves 

 emanating from the spinal cord to supply the extremities 

 and trunk. The sympathetic system is composed of two 

 ganglionated nerve cords extending throughout the 

 trunk within the body cavity, one on either side of the 

 vertebral column, and their various branches to all the 

 viscera, blood-vessels, etc., of the body (Figs. 91 and 92). 



THE BRAIN. 



The central nervous system is known as the cerebro- 

 spinal axis. It is composed of the brain and spinal cord. 

 The brain lies within the cranial cavity and is protected 

 by three membranes called the meninges. These may be 

 demonstrated by cutting away the roof of the skull with 

 the bone forceps. The dura mater is the tough fibrous 

 membrane lining the interior of the skull. It dips down 

 between the two halves of the cerebrum, forming the 

 falx cerebri. Between the cerebrum and cerebellum in 

 the cat it is ossified, thus forming the bony shelf or ten- 

 torium cerebelli (Fig. 18). The dura mater adheres 

 closely to the inner surface of the cranial cavity, forming 

 the internal periosteum. The second membrane of the 

 brain is the arachnoid. Between the dura mater and the 



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