The Dura Mater is the most general tissue of the body for it controls the body and is directly or indirectly in contact with all the tissues of the body. It is also a laminated covering and has as many as six laminations in some areas. It completely covers the brain and forms the Falx Cerebri and the tentorium which divides the brain into hemispheres, and the tentorium which separates the cerebrum and cerebellum. The Dura’s outer coat lines the cranium forming the pericranium and the Diploe of the cranium. The cerebrum functions with the world without, while the cerebellum functions with nature, the world within.
The Dura Mater is the third laminated covering of the brain, the cranium being the fourth or external covering. Being more remote from the brain it differs in force, power and perfection.
It is necessary that each of the brain coverings be laminated and there is an oleagenous fluid between them, for the inner layer and outer layer have respect at the same time to external and internal states of the brain and they feel in their own peculiar manner what is transacted in the brain.
The Dura Mater is the most general covering for it completely surrounds the brain, divides it into hemispheres, separates the cerebrum from the cerebellum, medulla oblongata, the pons and spinal structure and goes all the way down to the coccyx. It enters the sulci, forms the Sylvian and Rolando fissures, forms the Faix Cerebri, the tentorium, divides the cranium with its outer lamina as well as covering the fossae, protuberances, ridges and the various articulations of the cranial bones, even to the spiculae of their most delicate contacts. Thus nature goes forth from its center, the brain, to its circumferences from a simple to a compound structure, from purer to grosser and from active and purely elastic tissues, to inert and passive ones.
The motion or the flexion started in the brain or corticle substance by continuity of coverings, terminate in the cranium. The piamater sustains, governs and limits the particular motions of the brain; the dura, the more general, the cranium the most general. This motion in it self is alternate, the systolic motion of the brain, and is inherent in it. It is conspicuous in the brain itself and its membranes, but it is stopped and expires in the cranium. The expansile movement is palpable by the texture of the membranes. When the brain expands it folds up its clefts and Interstices and prevents the passage of the blood into the sinuses; it likewise draws down and contracts the sinuses themselves, hence the Dura in this respect is passive, yet by its elasticity and in its capacity as a muscular tendon it contributes in a general way as a reciprocal, expansion motion of the brain. (This was given by Leyden in 1740, proven by Key and Retzius in 1875) By its elasticity therefore, the Dura unites the brain to the centers of the cranium and the cranium to the poles of the brain.
There are three centers of the bones of the cranium: first, the frontal bone where the cresta galli is situated. Second, the middle of the occipital bone and third the basilar where the sella turcica lies. All the centers of the bones have respect to the poles for the poles of the brain are situated where the Falx begins, where the straight sinus emerges and where the pituitary gland is placed. We see how the action of the brain has respect to those places where the cranium is strongest and shocks received by the cranium are directed to the most tranquil places and thence are communicated to all parts of the whole brain without any fear of danger or injury. The brain protects itself by its own form, because whatever flows or runs in accordance to form, never injures or violates the mass.
The movement of the Dura conjoins the motion of the heart or the pulsation of its arteries with the motion of the brain or the animation of the fibers, for it undergoes a twofold motion, namely a pulsatory, which it derives from its own arteries, and expansile and constrictive, which is imparted to it by the brain (Pacchioni). We have this dual motion in the pleura, peritoneum and diaphragm, and in the pericardium. The motions of the brain and lungs coincide also. Exchange of arteries of the Dura with the brain is at the poles where it is quiescent.
The Dura is sensitive, has several nerves connecting it with the five senses. It is an elastic tendon and has many functions. It is also a continuation of the white (lymph) and red blood vessels. Its inner membrane is impregnated with a spiritus fluid from the nerves and when stretched or extended, recovers itself spontaneously. It greets each artery as it enters the skull, the muscular coat is released from the heart before the artery enters the skull as the Dura controls the circulation within the skull to keep an equilibrium within the skull of the blood supply to the brain.
The vertebral arteries enter the skull at the foramen magnum and form the posterior occipital artery. First they supply the cauda of the medulla oblongata, the olivary bodies and pyramids, ramify on the sides of the fourth ventricle producing the choroid plexus, spread over the surface of the whole cerebellum and insinuate themselves between the strata, always Invested by a duplicature of the piamater and are lost in the substance of the cerebellum.
The carotid artery enters the cranium at the carotid canal in the petrous portion of the temporal bone. Exteriorly this canal opens in the middle between the basilar process of the occipital bone and the styloid process, a short distance below the eustachian tube and enters the cranial cavity near the side of the sella turcica. It enters and ascends into the cerebrum through a foramen In the cavernous sinus.
The pneumogastric nerve leaves the cranium through the carotid canal or foramen. In crossing, it is attached to the carotid by cellular filaments or by way of filaments in the form of plexes creeping through its adscititious coating. Just outside the canal it communicates with the superior cervical ganglion of the sympathetic nervous system, the vagus passing between the artery and vein. This gives the Dura control of all three nerve systems and control of the blood so that Incase the carotid is insufficient the Dura can so control the blood and have the vertebral take over the deficiency. Thus the Dura is connected with the control of the blood, harmonizes with the nerves and controls the spiritous fluids secreted by the brain and relates itself to the mucous membranes through its contact with the orbits, ears, nose and sensory specializations and through the pneumogastric and hence the digestive system.
It is the general connecting link with the brain and body for when badly injured or cut, the falx and tent become flaccid and the patient succumbs.
The Dura is elastic, yet a passive membrane, made of a very strong tendonous structure covering the brain in its entirety and responds to the brain in its activity, so it necessarily consists of arteries, veins and tendonous fibres. It is a laminated tissue, as are all the coverings to the brain, the outer lamina being the most vascular, hence its fibers are compact for it contains vessels of red and white blood serum, lymph, as well as fibers of nerves.
The inner lamina consists of ducts or tubes which convey nervous secretions and a large supply of blood to the periostium. It is really the internal lamina that is more elastic as it poises the motion of the sinuses and by virtue of its elasticity may reach, yet at the same time act upon, the inflowing and out flowing vessels, for when this lamina is Injured its elasticity is impaired, and its effects also perish.
Since the Dura is elastic it recovers itself spontaneously. It receives the new secretions of the brain and that which is in it at the time it cannot discharge. This gives rise to its reactive power. The internal lamina is more elastic than the external for it poises the motion of the sinuses.
The motions of the spinal cord and cerebrum cause the superfluous nervous secretions to return from the body to be propelled the pumped toward the Dura Mater and at the same time toward the pericranium. This is evident if this membrane is examined in the spinal cord where, in its front part it is conjoined with the ligamentary coating in the neck and the atlas, where it is articulated with the occiput, as the Dura is moved when the cerebrum is in a state of motion. The road taken by the fluid from the foramen magnum is toward the sphenoid bone laterally up into the Dura itself, where it is loosely adjoined to the cranium. The Dura here is doubled (Falx Cerebri) and is carried along the longitudinal sinus and thereby acted upon by both sides propelling the secretions forward. The greatest portion of the nervous fluids go into the tentorium and thence upward in the direction taken by the fibers obliquely from front to back so the dura gets its blood supply. The Pacchinian glandules are small elevations chiefly of the pia and arachnold because between the longitudinal sinus and the piamater are vessels, muscular bands and little cords causing these grains or miliary corpuscles to arise. The pearl in the oyster. (Quaines Anatomy)
Key and Retzius found that most of the pacchionian bodies are contained in venous lacunae, on either side of the longitudinal sinus and that the refined lymph which is conveyed to them by the arachnoidea oozes out through the surface of the pacchionian gland, thus mixing with the venous blood which empties into the longitudinal sinus.
The Falx Cerebrae starts at the cresta galli where it is attaches as through by a nail and goes back to the middle of the occiput. Thus under the saggital suture, the Dura holds the longitudinal sinus in suspension and then lets Itself down to the corpus callosum forming the hemispheres of the brain. Here also It forms and holds in suspension the inferior longitudinal sinus which is sometimes inserted in its duplicature. From its origin it gradually increases in height and thickness until it reaches the region of the straight sinus to which it is united obliquely and in lateral extension with the center of the tentorium which separates the cerebrum from the cerebellum.
The internal lamina of the dura on both sides concurs in the formation of the falx or first process of the Dura and applies itself to it so that is why the sinus and veins are said to be contained within its duplicature.
The external or superior lamina spreads over the sinus and is continued into that of the opposite side, arising as it does from the cresta galli; then from the osseous lamina into which it is produced backward, it cleaves the olfactory nerves and the anterior part of the cerebrum. Thence it follows an upward direction towards the torcula herophilii where it unites with the tentorium. It has close membranous connections with the cranium in those places under the sutures and with the brain itself by the intervention of the piamater to which it is joined by large blood vessels. It is propagated thence to the longitudinal and lateral sinuses as it descends between the two hemispheres of the cerebrum and afterwards to the back of the corpus cellosum. Over this it is loosely expanded and by ramifications of blood vessels terminates in the interior longitudinal sinus.
The union of the Falx and tent keeps them both very tense so they are able to sustain considerable weight and the falx capable of resisting laternal pressures without giving to right or left. Hence these are reciprocal tension membranes in their natural state. Both are sickle shaped and if either one is cut, both become flaccid.
The tentorium or lateral second processes of the Dura embrace the lowest portion of the cerebrum and the highest of the cerebellum, for these two lateral processes near the straight sinus receive the falx, which is above and continues them. The tentorium spreads at right angles to the falx, first following the groove in the occipital bone of the lateral sinus then on to the petrous portion. But below, beside the corpora quadrigemenia, around the medulla oblongata which it engirdies, it tends by a shorter route, horizontally, towards the cerebrum. The tentorium is a four fold and not a two fold membrane, hence furnishing a very strong couch and pavement for the cerebellum which lies underneath. Hence each brain is prevented from injuring the other. The two brains have different functions but work in rhythm and harmony throughout.The Dura Mater (reprint)