 dura mater ( or ), or dura, is a thick membrane that is the outermost of the three layers of the meninges that surround the brain and spinal cord. it is derived from mesoderm. the other two meningeal layers are the pia mater and the arachnoid mater. the dura surrounds the brain and the spinal cord and is responsible for keeping in the cerebrospinal fluid. ==structure== thumb|left the dura mater has several functions and layers. the dura mater is a sac (aka thecal sac) that envelops the arachnoid mater. it surrounds and supports the dural sinuses (also called dural venous sinuses, cerebral sinuses, or cranial sinuses) and carries blood from the brain toward the heart. the dura mater has two layers, or lamellae: the superficial layer (also called the periosteal layer), which serves as the skull's inner periosteum, called the endocranium; and a deep layer called the meningeal layer; the actual dura mater. ===dural folds and reflections=== thumb|right|spinal reflections and folds. the dura separates into two layers at dural reflections (also known as dural folds), places where the inner dural layer is reflected as sheet-like protrusions into the cranial cavity. there are two main dural reflections: * the tentorium cerebelli exists between and separates the cerebellum and brainstem from the occipital lobes of the cerebrum.shepherd s. 2004. "head trauma." emedicine.com. * the falx cerebri, which separates the two hemispheres of the brain, is located in the longitudinal cerebral fissure between the hemispheres.vinas fc and pilitsis j. 2004. "penetrating head trauma." emedicine.com. two other dural infoldings are the cerebellar falx and the sellar diaphragm: * the cerebellar falx (or falx cerebelli) is a vertical dural infolding that lies inferior to the cerebellar tentorium in the posterior part of the posterior cranial fossa. it partially separates the cerebellar hemispheres. * the sellar diaphragm is the smallest dural infolding and is a circular sheet of dura that is suspended between the clinoid processes, forming a partial roof over the hypophysial fossa. the sellar diaphgram covers the pituitary gland in this fossa and has an aperture for passage of the infundi
Meninges