INTRASPINAL VESSELS. 385 



behind the bodies of the two contiguous vertebras, and join in anastomotic 

 loops with an offset of the intraspinal artery above and below. And from 

 the loops offsets (d) are furnished to the periosteum and the bodies of the 

 vertebrae. Anastomotic twigs connect the arches across the vertebra. 



The intraspinal vessels produce also a central longitudinal artery (e), 

 like that on the front of the spinal cord, which lies on the bodies' of the 

 vertebrae, and is reinforced at intervals by offsets from the loops. 



The intraspinal veins (fig. 128) consist of two anterior longitudinal 

 vessels, which extend the whole length of the spinal canal ; of veins inside 

 the bodies of the vertebrae ; and of a plexus of veins beneath the neural 

 arches. 



The anterior longitudinal (a) are close to the bodies of the vertebrae, 

 one on each side of the posterior common ligament ; and they are irregu- 

 lar in outline, owing to certain constrictions near the intervertebral fora- 

 mina. They receive opposite the body of each vertebra the veins (c ) from 

 that bone ; and through the intervertebral foramina they have branches of 

 communication (a) with the veins outside the spine in the neck, the dorsal 

 region, the loins, and the pelvis. 



Veins of the bodies of the vertebrce. Within the canals in the bodies of 

 the vertebrae are large veins, which join on the front of the bone with 

 veins in that situation. Towards the back of the body they are united in 

 an arch, from which two trunks issue by the large apertures on the poste- 

 rior surface. Escaped from the bone, the trunks diverge to the right and 

 left, and open into the longitudinal veins. 



The posterior spinal veins form a plexus between the dura mater and 

 the arches of the vertebrae. A large vein may be said to lie on each side 

 of the middle line, which joins freely with its fellow, and with the ante- 

 rior longitudinal vein by lateral branches. Offsets from these vessels are 

 directed through the intervertebral foramina, to end in the veins (a) at the 

 roots of the transverse processes. 



