The outermost meninges are known as which of the following?

The outermost meninges are known as the dura mater. This tough protective layer serves as the first line of defense for the brain and spinal cord, safeguarding them from mechanical injury and infection. The dura mater is a durable membrane that is not only essential for protection but also plays a role in containing cerebrospinal fluid, which cushions the central nervous system.

The other options refer to different layers of the meninges or are incorrect terms. The arachnoid is the middle layer and provides a web-like structure that includes the subarachnoid space for cerebrospinal fluid. The pia mater is the innermost layer that closely adheres to the surface of the brain and spinal cord, providing additional protection and support. The term 'duramoid' does not correspond to any recognized meninges in medical terminology; it may cause confusion as it is not commonly utilized in the context of the protective membranes surrounding the central nervous system.