The combining form that denotes the outermost meningeal layer is which?

• A. Cephal/o
• B. Gingiv/o
• C. Ventri/o
• D. Dur/o

Answer: (D)

The outermost protective covering of the brain and spinal cord is the dura mater. The combining form dur/o denotes this dura mater, so it’s the correct choice. The other forms don’t relate to the meninges: cephal/o means head, gingiv/o means gums, and ventri/o refers to the belly or to brain ventricles, not to the dura. Understanding the three meninges in order—dura mater (outer), arachnoid mater (middle), and pia mater (inner)—helps see why dur/o is the appropriate combining form for the outer layer.