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Structure. The cranial dura mater consists of white fibrous tissue and elastic fibers arranged 

 in flattened laminae which are imperfectly separated by lacunar spaces and bloodvessels into 

 two layers, endosteal and meningeal. The endosteal layer is the internal periosteum for the 

 cranial bones, and contains the bloodvessels for their supply. At the margin of the foramen 

 magnum it is continuous with the periosteum lining the vertebral canal. The meningeal or 

 supporting layer is lined on its inner surface by a layer of nucleated flattened mesothelium, 

 similar to that found on serous membranes. 



The arteries of the dura mater are very numerous. Those in the anterior fossa are the anterior 

 meningeal branches of the anterior and posterior ethmoidal and internal carotid, and a branch 

 from the middle meningeal. Those in the middle fossa are the middle and accessory meningeal 

 of the internal maxillary; a branch from the ascending pharyngeal, which enters the skull through 

 the foramen lacerum; branches from the internal carotid, and a recurrent branch from the lacrimal. 

 Those in the posterior fossa are meningeal branches from the occipital, one entering the skull 

 through the jugular foramen, and another through the mastoid foramen; the posterior meningeal 

 from the vertebral; occasional meningeal branches from the ascending pharyngeal, entering the 

 skull through the jugular foramen and hypoglossal canal; and a branch from the middle meningeal. 



The veins returning the blood from the cranial dura mater anastomose with the diploic veins 

 and end in the various sinuses. Many of the meningeal veins do not open directly into the sinuses, 

 but indirectly through a series of ampulla?, termed venous lacunae. These are found on either 

 side of the superior sagittal sinus, especially near its middle portion, and are often invaginated 

 by arachnoid granulations; they also exist near the transverse and straight sinuses. They 

 communicate with the underlying cerebral veins, and also with the diploic and emissary veins. 



The nerves of the cranial dura mater are filaments from the semilunar ganglion, from the 

 ophthalmic, maxillary, mandibular, vagus, and hypoglossal nerves, and from the sympathetic. 



The Spinal Dura Mater (dura mater spinalis; spinal dura) (Fig. 767) forms a 

 loose sheath around the medulla spinalis, ahd represents only the inner or meningeal 

 layer of the cranial dura mater; the outer or endosteal layer ceases at the foramen 

 magnum, its place being taken by the periosteum lining the vertebral canal. The 

 spinal dura mater is separated from the arachnoid by a potential cavity, the sub- 

 dural cavity; the two membranes are, in fact, in contact with each other, except 

 where they are separated by a minute quantity of 

 fluid, which serves to moisten the apposed surfaces. 

 It is separated from the wall of the vertebral canal 

 by a space, the epidural space, which contains a quan- 

 tity of loose areolar tissue and a plexus of veins; the 

 situation of these veins between the dura mater and 

 the periosteum of the vertebrae corresponds therefore 

 o that of the cranial sinuses between the meningeal 

 and endosteal layers of the cranial dura mater. The 

 spinal dura mater is attached to the circumference of 

 the foramen magnum, and to the second and third 

 cervical vertebrae; it is also connected to the pos- 

 terior longitudinal ligament, especially near the lower 

 end of the vertebral canal, by fibrous slips. The 

 subdural cavity ends at the lower border of the second 

 sacral vertebra; below this level the dura mater closely 

 invests the filum terminate and descends to the back of 

 the coccyx, where it blends with the periosteum. The 

 sheath of dura mater is much larger than is necessary 

 for the accommodation of its contents, and its size is 

 greater in the cervical and lumbar regions than in 

 the thoracic. On each side may be seen the double 

 openings which transmit the two roots of the corre- 

 sponding spinal nerve, the dura mater being continued 

 in the form of tubular prolongations on them as they pass through the interverte- 

 bral foramina. These prolongations are short in the upper part of the vertebral 

 column, but gradually become longer below, forming a number of tubes of fibrous 

 membrane, which enclose the lower spinal nerves and are contained in the verte- 

 bral canal. 



FIG. 767. The medulla spinalis and 

 Us membranes. 



bral cana 



