PMC

FIG. Diagram demonstrating the formation of the double-layered tela choroidea (velum interpositum) of the third ventricle in the human.
1) The developing neural tube includes the forebrain (FB) which is surrounded by the pia mater (broken line).
2) and 3) The expanding vesicle of the cerebral hemisphere (HV) carries its own pia mater (b) which overlaps the pia mater (a) of the third ventricle. IF signifies intraventricular foramen.
4) A double layer of pia mater (b, a) is interposed between the two cerebral vesicles and the third ventricle (3V). E signifies ependyma.
5) The two layers of pia mater (b, a) over the third ventricle persist after connection of the hemispheres by the commissures.

A) Graphic showing the anatomy of the perivascular space surrounding the artery (periarteriolar space). The gray area represents subarachnoid space while the beige area represents brain parenchyma. An artery (asterisk) is passing from the subarachnoid space into the brain parenchyma. The periarteriolar space (yellow area as shown by the short thick arrow) is between the artery and the pia mater (long thin arrow). The subpial space (turquoise area shown by double short arrows) is separated from periarteriolar space by the pia mater which extends along the artery. B) Graphic showing the anatomy of the perivascular space surrounding the vein (perivenular space). The gray area represents the subarachnoid space while the beige area represents brain parenchyma. A vein (double asterisks) is passing from the brain parenchyma into the subarachnoid space. Unlike the periarteriolar space which is separated from the subpial space by the pia mater, the perivenular space (yellow area as shown by the short thick arrow) is continuous with the subpial space, as the pia mater (long thin arrow) does not extend along the vein within the brain parenchyma as a continuous sheath.

trkA-like immunoreactivity in the pia mater. The micrographs show immunohistochemical detection of trkA at the surface of the uninjured adult cat (A) and rat (B, C) lumbar spinal cord. The arrows indicate labeling in the pia mater. Thin cell process associated with blood vessels extend into the spinal cord (arrowheads). InC, trkA-LI is seen in the pia mater in the ventral fissure and in the pia mater surrounding a blood vessel. Scale bars, 50 μm.

The finite element model of a generic human thoracic spinal cord. Grey and white matter materials were modeled using eight-node, plane-strain, hybrid elements. Pia mater was modeled using three-node truss elements.