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. 105 and 106). 



THE BRAIN 



The central nervous system is known as the cerehro-spinaJ 

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

 lies within the cranial cavity and is protected by three mem- 

 branes 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/a/o; cerebri. Between the cerebrum and cerebellum 

 in the cat it is ossified, thus forming the bony shelf or tentorium 

 cerebelli (Fig. 19). The second membrane of the brain is the 

 arachnoid. Between the dura mater and the arachnoid is 

 the subdural space, containing a fluid having the nature of the 

 aqueous humor. The arachnoid is a very delicate membrane 

 which does not dip down into the clefts between the folds of the 

 brain, as is the case with the pia mater, but passes across these 

 depressions, where it may be easily demonstrated (Fig. 109). 



The subarachnoidal space lies between the arachnoid and pia 

 mater. The pia mater is the delicate vascular membrane follow- 



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