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 and 95). 
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 falx 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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