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. 94 



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 demon- 

 strated 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 jalx cerebri. Be- 

 tween the cerebrum and cerebellum in the cat it is ossified, 

 thus forming the bony shelf or tentorium cerebelli (Fig. 

 18). 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 lymph. 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 de- 

 pressions, where it may be easily demonstrated (Fig. 98). 



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