ASkeletal Coverings

(1) Brain. The bones of the cranium form a spherical case around the brain. The cranial cavity is the space enclosed by the bones of the cranium.

(2) Spinal cord. The vertebrae, with the vertebral foramina, form a cylindrical case around the spinal cord. The overall skeletal structure is the vertebral column (spine). The vertebral (spinal) canal is the space enclosed by the foramina of the vertebrae.

b. Meninges (Fibrous Membranes). The brain and spinal cord have three different membranes called meninges surrounding them (Figure 5-8). These coverings provide protection.

(1) Dura mater. The dura mater is a tough outer covering for the CNS. Beneath the dura mater is the subdural space, which contains a thin film of fluid.

Figure 5-8. The meninges, as seen in side view of the CNS.

(2) Arachnoid mater. To the inner side of the dura mater and subdural space is a fine membranous layer called the arachnoid mater. It has fine spider-web type threads that extend inward through the subarachnoid space to the pia mater. The subarachnoid space is filled with cerebrospinal fluid (CSF).

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