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564 THE NERVOUS SYSTEM. 
sheaths from the pia mater. These blend with the connective-tissue sheaths of 
the nerves. q 
The ligamentum denticulatum is a strong fibrous band which stretches out 
like a wing from the pia mater on either side of the spinal cord, so as to connect 
the pia mater with the dura mater. The pial or inner attachment of the ligament 
extends in a continuous line between the anterior and posterior nerve- roots, from 
the level of the foramen magnum above to the level of the first lumbar vertebra 
below. Its outer margin is serrated or denticulated, and for the most part free. 
From twenty to twenty-two denticulations may be recognised. They occur in the 
intervals between the spinal nerves, and pushing the arachnoid before them, they 
are attached by their pointed ends to the inner surface of the dura mater. The — 
ligamenta denticulata partially subdivide the wide subarachnoid space in the spinal 
canal into an anterior and a posterior compartment. The anterior nerve-roots 
traverse the anterior compartment, whilst the posterior nerve-roots traverse the 
posterior compartment. Further, the posterior compartment is imperfectly sub-_ 
divided into a right and a left lateral part by the septum posticum. 
By means of the ligamenta denticulata the spinal cord is suspended in the 
middle of the tube of dura mater. 
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