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==Arachnoid mater==

==Arachnoid mater==

This is the middle meningial layer and lies between the dura mater and the pia mater, the innermost meningeal layer. The arachnoid mater is a delicate structure and is constructed with non-vascular connective tissue. This layer also has small protrusions through the dura mater into the previously mentioned venous sinueses and allow cerebrospinal fluid (CSF) to enter and exit the blood stream. These protrusions adhere to the inner surface of the skull via ''calvaria'' processes.

This is the middle meningial layer and lies between the dura mater and the pia mater, the innermost meningeal layer. The arachnoid mater is a delicate structure and is constructed with non-vascular connective tissue. This layer also has small protrusions through the dura mater into the previously mentioned venous sinueses called '''Arachnoid villus''' and these allow cerebrospinal fluid (CSF) to enter and exit the blood stream. These protrusions adhere to the inner surface of the skull via ''calvaria'' processes.

The subarachnoid space lies between the arachnoid mater and pia mater. Both meninges are connected via a fine network of connective tissue filaments (spider-like) which run through the space, originating from the arachnoid mater. This space also contains CSF from ventricular system. The largest part of this space are called the ''cisterns'' which are used for the collection of CSF. For example there is a cerebellomedullary cistern around the foramen magnum. The lumbar cistern used for lumbar puncture in man.  

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*# Pia mater

*# Pia mater

*#* highly vascular connective tissue, very closely applied to brain tissue

*#* highly vascular connective tissue, very closely applied to brain tissue