630 



NERVOUS SYSTEM. (NERVOUS CENTRES. THE MENINGES.) 



In front of the dura mater and situate between 

 the outer edge of the posterior common liga- 

 ment of the vertebrae and the pedicles, we find 

 two remarkable venous sinuses which extend the 

 whole length of the vertebral column, from the 

 occipital foramen to the sacral region (Jig. 360). 



Fig. 360. 



Spinal sinuses viewed from before. 

 (After Breschet.) 



The anterior part of the basis cranii and the face 

 have been removed, as also the bodies of the 

 vertebrae. 



/, lateral sinus descending to form its junction 

 with the jugular vein; c, cavernous sinus; v, ver- 

 tebral artery, the longitudinal sinuses with their 

 transverse connecting veins, lying immediately be- 

 hind the bodies of the vertebrae. The interior 

 petrosal and the cavernous sinuses appear like con- 

 tinuations of them within the cranium, and the 

 transverse and circular sinuses are analogous to the 

 transverse spinal branches. 



These veins are loosely covered by a thin pro- 

 cess, which is prolonged from each margin of 

 the posterior common ligament, and which is 

 sufficiently transparent to allow them to be seen 

 through it without removing it. They have 

 been known since the time of Fallopius, and 

 were described by Willis as the longitudinal 

 spinal sinuses. In calibre they present many 

 inequalities, being dilated at one part and con- 

 stricted at another, according to the number 

 and size of the vessels which communicate 

 with them. The sinuses of opposite sides run 

 parallel to each other and communicate by cross 

 branches, which pass between the posterior sur- 

 face of the body of each vertebra and the pos- 



terior common ligament. These cross branches 

 present the same characters as the sinuses them- 

 selves, being of variable calibre, and presenting 

 the greatest degree of dilatation at their middle. 

 At tin's point these branches receive veins which 

 emerge from the spongy texture of the bodies of 

 the vertebrae (basi-vertebral veins of Breschet) 

 (fig. 361, d). The vertebral sinuses diminish in 



Fig. 361. 



Sasi-vertebral veins, converging from the spongy struc- 

 ture of the body of the vertebra. 



size at the highest part of the vertebral canal, and 

 passing through the anterior condyloid foramina, 

 communicate with the internal jugular veins. 

 In the sacral region they diminish considerably 

 likewise, and are lost in becoming continuous 

 with the lateral sacral veins and other small 

 veins in that region ; and they communicate 

 with the deep and superficial vertebral veins in 

 the neck, with the intercostal veins in the back, 

 and with the lumbar ones in the loins. They 

 evidently differ from the sinuses of the cranial 

 dura mater in not being enclosed between two 

 layers of fibrous membrane as those vessels are. 



Bloodvessels of the cranial dura mater. 

 The bloodvessels of the cranial dura mater 

 are much more numerous than those of the 

 spinal, in consequence, no doubt, of that mem- 

 brane performing the office of a periosteum to 

 the cranial bones. The arteries are derived 

 from numerous sources ; in front from the 

 ophthalmic and ethmoidal arteries, in the 

 middle from the internal maxillary artery by 

 the middle meningeal, which enters the cranium 

 at the foramen spinosum, and by small branches 

 from the internal carotid which have been 

 called inferior meningeal arteries. Posteriorly 

 the vertebral, the occipital, and the ascending 

 pharyngeal supply branches which go by the 

 name of posterior meningeal arteries. 



The veins of the dura mater are formed simi- 

 larly to those in other parts, being derived from 

 radicles which take their rise in the membrane 

 itself as well as from the osseous walls of the 

 cranium, from the diploi'c veins of those bones. 

 (See BoNE,/gs. 187, 188, vol. i.) All of them, 

 with the occasional exception of one or two 

 which accompany the middle meningeal artery 

 and pass out at the foramen spinosum, pour 

 their blood into the great venous canals en- 

 closed between the laminae of the dura mater, 

 which are called Sinuses. 



