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The dura mater is a thick and dense inelastic fibrous membrane, which lines the interior of the skull. Its outer surface is rough and fibrillated, and adheres closely to the inner surface of the bones, forming their internal periosteum; this adhesion being more intimate opposite the sutures and at the base of the skull, where it is attached to the margin of the foramen magnum, and is here continuous with the dura mater lining the spinal canal. Its inner surface is smooth and epithe-liated, being lined by the parietal layer of the arachnoid. The dura mater is therefore a fibre-serous membrane, composed of an external fibrous lamella, and an internal serous layer. It sends numerous processes inwards, into the cavity of the skull, for the support and protection of the different parts of the brain; it is also prolonged to the outer surface of the skull, through the various foramina which exist at its base, where it is continuous with the pericranium, and its fibrous layer forms sheaths for the nerves which pass through these apertures. At the base of the skull, it sends a fibrous prolongation into the foramen caecum; it lines the olfactory groove, and sends a series of tubular prolongations around the filaments of the olfactory nerves as they pass through the cribriform foramina; a prolongation is also continued through the sphenoidul fissure into the orbit, and another is continued into the same cavity through the optic foramen, forming a sheath for the optic nerve, which is continued as far as the eye-ball. In certain situations in the skull already mentioned, the fibrous layer of this membrane subdivides into two, to form the sinuses for the passage of venous blood. Upon the upper surface of the dura mater, in the situation of the longitudinal sinus, may be seen numerous small whitish bodies, the glandulae Pacchioni.
Structure. The dura mater consists of white fibrous and elastic tissues, arranged in flattened laminae, which intersect one another in every direction.
Its arteries are very numerous, but are chiefly distributed to the bones. Those found in the anterior fossa, are the anterior meningeal, from the anterior and posterior ethmoidal, and internal carotid. In the middle fossa are the middle and small meningeal, from the internal maxillary, and a third branch from the ascending pharyngeal, which enters the skull through the foramen lacerum basis cranii. In the posterior fossa, are the posterior meningeal branch of the occipital, which enters the skull through the jugular foramen, the posterior meningeal, from the vertebral, and occasionally meningeal branches from the ascending pharyngeal, which enter the skull, one at the jugular foramen, the other at the anterior condy-loid foramen.
The veins which return the blood from the dura mater and partly from the bones, anastomose with the diploic veins. These vessels terminate in the various sinuses, with the exception of two which accompany the middle meningeal artery: these pass from the skull at the foramen spinosum.
The nerves of the dura mater, are the recurrent branch of the fourth, and filaments from the Gasserian ganglion, the ophthalmic nerve, and sympathetic.
The so-called Glandulas Pacchioni are numerous small whitish granulations, usually collected into clusters of variable size, which are found in the following situations: I. Upon the outer surface of the dura mater, in the vicinity of the superior longitudinal sinus, being received into little depressions on the inner surface of the calvarium. 2. On the inner surface of the dura mater. 3. In the superior longitudinal sinus. 4. On the pia mater near the margin of the hemispheres.
These bodies are not glandular in structure, but consist of a fibro-cellular matrix originally developed from the pia mater: by their growth they produce absorption or separation of the fibres of the dura mater; in a similar manner they make their way into the superior longitudinal sinus, where they are covered by the lining membrane. The cerebral layer of the arachnoid in the situation of these growths is usually thickened and opaque, and adherent to the parietal portion.
These bodies are not found in infancy, and very rarely until the third year. They are usually found after the seventh year; and from this period they increase in number as age advances. Occasionally they are wanting.
Medicine: The stomach
Critical care
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