DURA MATER.
The dura mater consists of two lamellae. The outer lamella, which lies against the bone and serves as the inner periosteum of the cranial case, consists of soft, loose vascular connective tissue. The inner lamella is denser, made up of fibrous connective tissue, and contains few blood-vessels. While the outer layer appears as periosteum and is prolonged on the cerebral nerves as robust sheaths, the inner layer comes into closer relation with the brain, since it sends processes between the larger divisions of the brain. Such processes are i. The falx cerebri, or falx cerebri major, which, penetrating between the spheres, begins in front at the crista galli, attached by its convex upper border to the sides of the sulcus sagittalis of the cranial vault, and extends backward as far as the protuberantia occipitalis interns. Between the outer and inner lamellae, along the upper convex border of the falx, is a blood-space, which is triangular in cross-section and known as the sinus sagittalis superior. The lower concave border of the sickle-like falx is free and encloses the smaller sinus sagittalis inferior. From the internal occipital protuberance forward, the falx is attached to the tent-like tentorium cerebelli, the line of junction being the tent-edge, while the border attached to the crista galli is the crest-edge. In front, the falx only incompletely separates the two frontal lobes, but behind its height is so increased, that it penetrates almost, but not quite, to the upper surface of the corpus callosum.
2. The falx cerebelli, or falx cerebri minor, which forms a small sagittal pro longation of the large falx, penetrates between the cerebellar hemispheres and descends from the internal occipital protuberance to the foramen magnum. The convex border
encloses the sinus occipitalis and is attached along the crista occipitalis. Corresponding to the terminal limits of the crest, the cerebellar falx divides into two diverging arms, which enclose the continuations of the sinus occipitalis.
3. The tentorium cerebelli, which forms a dorsally arched transverse partition between the basal surface of the occipital lobes of the cerebrum and the dorsal surface of the cerebellum. The outer convex margin is attached, on each side, along the lineae transversae of the occipital and parietal bones, where it encloses the sinus transversus, and along the dorsal edge of the portion of the temporal bone, where it conveys the sinus petrosus superior. Thence the attachment of the tentorium passes to the pro cessus clinoides anterior. In front, the free inner margin of the tentorium meets the outer one and then extends backward and slightly upward to unite with the lower edge of the falx cerebri. Along this line of union lies the sinus rectus, which in front receives the vena cerebri magna Galeni (Fig. 55) and behind opens into the con/Thetis sinuum or the torcular Herophili.
4. The diaphragms sellae turcicae, which forms a bridge of dural tissue over this depression in the sphenoid bone. Between the basal and dorsal lamella: of the diaphragma sellae turcicae lies the hypophysis or pituitary body. An opening in the middle of the membrane, the foramen diaphragmatis, affords passage to the infundibulum.