THE VEINS OF THE SPINE. 



533 



back, and form a plexus over the arches of the vertebrae. The largest tributaries 

 pass forwards by the side of the interspinous ligaments, proceeding in many cases 

 from a median longitudinal vessel placed over the spinous processes of several 

 vertebras. Offsets from the plexus perforate the ligamenta subflava to join the 

 posterior longitudinal veins within the spinal canal ; and at the outer part of the 

 vertebral groove other veins are given off, which pass forwards between the trans- 

 verse processes and open into the posterior branches of the intercostal and lumbar 

 veins, or in the neck, where the plexus is most developed, into the vertebral vein. 



The veins of the bodies of the vertebrae are comparatively Harge vessels 

 contained in the canals within these bones, the arteries which accompany them 

 being very small. They anastomose on the front of the vertebras with the veins in 

 that situation ; and the trunk of each, having reached the spinal canal through the 

 single or double foramen on the posterior surface of the body of the vertebra, opens 

 into the corresponding transverse branch uniting the anterior longitudinal veins. 



Fig. 412, A and B. HORIZONTAL AND SAGITTAL SECTIONS OP 



LOWER DORSAL VERTEBRA, SHOWING THE EXTERNAL AND 

 INTERNAL VEINS OF THE SPINE. (Breschet.) | 



a, spinous process ; 6, transverse process ; c, body ; d, spinal 

 canal ; 1 , external veins of the body ; 2, dorsal spinal veins, com- 

 municating with the internal and forming a plexus over the laminae 

 and processes ; 3, posterior, and 4, anterior internal plexus of 

 veins of the spinal canal ; 5, internal veins of the body joining 

 the anterior spinal veins ; 6, posterior branches of the intercostal 

 veins. 



The anterior longitudinal spinal veins are two 



large plexiform vessels which extend the whole length 

 of the spinal canal, lying behind the bodies of the 

 vertebrae, one along each edge of the posterior 

 common ligament. These vessels are dilated opposite 

 the bodies of the vertebrae, where the right and left 

 veins are connected by large transverse branches placed 

 between the posterior common ligament and the bones, 

 and constricted over each inter vertebral disc, at which 

 point an offset is sent outwards through the corre- 

 sponding intervertebral foramen. Superiorly, the 

 anterior spinal veins, having given off a large offset 



above the atlas to form the beginning of the vertebral vein, communicate with 

 the basilar sinus through the foramen magnum, and form, with the posterior spinal 

 veins and the lower end of the occipital sinus, a venous ring in the substance of 

 the dura mater round that opening. 



The posterior longitudinal spinal veins, also two in number, are contained 

 in the loose tissue between the dura mater and the posterior wall of the spinal 

 canal. They are often much broken up in parts of their course, and they communi- 

 cate with one another by numerous cross branches on the anterior surface of the 

 arches of the vertebrae, with the dorsal spinal veins by branches perforating the 

 ligamenta subflava, and with the occipital sinus by branches which ascend through 

 the foramen magnum. From the plexus thus formed offsets pass outwards to the 

 intervertebral foramina, where they join the similar branches given off by the 

 anterior longitudinal veins, and form a plexus around the issuing nerve. 1 



The veins of the spinal cord are of small size and run with a tortuous course 

 in the substance of the pia mater, where they form a network with elongated 



1 C. Walther, op. cit. ou p. 512. 



M M -1 



