SPINAL 



629 



into the meningeal and the medullary. The meningeal form an anterior and a 

 ])(>sterior spinal plexus between tlic (hira mater and the walls of the s])inal canal, 

 and are generally known as the meningo-rachidean veins. They receive the veins 

 from the bodies of the vertebrse. The medullary set are situated within the dura 

 mater; they return the l)lood from the S])inal cord, and are kncjwn as the mcdulli- 

 spinal veins. 



1. The extraspinal veins. — (a) The veins of the anterior spinal plexus 

 ramify in front of the bodies of the vertebra?. They are of small size and most 

 distinct in the cervical region (fig. 890). They open into the neigh})ourmg veins. 



(h) The veins of the posterior spinal or dorsal spinal plexus are situated 

 around the spinous processes, the laminse, and the articular and transverse ])r()- 

 cesses of the verteljroe, the larger veins of the plexus running horizontally forwards 

 along the interspinous ligaments. The plexus is formed chiefly by the union of 

 tributaries proceeding from the integuments of the back and the spinal muscles. 



Fig. 390.— The Spixal Veins. 



ACCESSORY PRO- 

 CESS OR TIP 

 OF THE TRUE 

 TRANSVERSE 

 PROCESS 



COSTAL ELEM 



Posterwr traiisrerse 



branch 



Vein from cord 

 Transverse branch 



A iilerior transverse 

 rein 



Lumbar vein 



Dorsal spinal pleitis 



Branch 

 jiKrJoraling 

 ligamenla 

 subjiara 

 Posterior longitudinal 



spinal vein 

 Lateral transverse 



branch 

 A nterior longitudin al 

 spinal vein seen in 

 section 

 Vdn.i from body of 

 vertebra 



Anli-rior spinal plexus 



C'onnnunications take place between the veins of each vertebral segment by vertical 

 t)ranches running upwards and downwards to the })lexus above and below respec- 

 tively near tlie base of the transverse ])roces.ses. Branches are also sent through 

 the ligamenta suV)flava between the laminie of the several vertebra* to the posterior 

 plexus of the intrasjdnal veins, and also forwards l)etween tlie transverse processes 

 of the vertebrie to join the vertebral vein in the neck, the dorsal branch of the 

 intercostal veins in the thorax, the lumV)ar veins in the lumbar region, and the 

 lateral sacral veins in the sacral region. 



2. The intraspinal veins are divided into (a) the meningeal; and (h) the 

 medullary, or meduUi-spinal. 



{'I) The meningeal extra-medullary or meningo-rachidian veins lie in 

 the fatty tissue between the walls of tlie verteliral canal and the dura mater or 

 theca vertebralis. They are arranged in four longitudinal channels, two of which 

 are anterior and two posterior, united by transverse branches corresponding in 

 numlier to the vertebral segments (fig. 390). 



