1332 A MANUAL OF ANATOMY 



given off, which anastomose with adjacent offsets of contiguous 

 transverse branches, and in this manner a median longitudinal 

 anastomotic chain is formed on the backs of the bodies of the 

 vertebrae. There are thus three longitudinal chains on the posterior 

 surfaces of the bodies of the vertebrae, one being median and two 

 Lateral. From these chains branches are furnished to the bodies of 

 the vertebrae and their ligaments. The posterior parietal branch of 

 each side passes to the front of a lamina, where it acts in a manner 

 similar to the anterior parietal branch. Two posterior longitudinal 

 anastomotic chains are thus constructed in front of the laminae, one 

 at either side, which communicate at frequent intervals by trans- 

 verse branches, and from these sources offsets are furnished to the 

 laminae and ligamenta subflava. 



Arteries of the Spinal Cord. — ^These are : (i) the anterior spinal 

 artery ; (2) the posterior spinal arteries, right and left ; and (3) the 

 lateral spinal arteries, right and left (neural or central branches 

 just described in connection with the spinal canal). 



The anterior spinal artery is formed by the union of the anterior 

 spinal branches, right and left, of the vertebral arteries. It descends 

 along the front of the cord in the median line, and is reinforced at 

 regular intervals by the lateral spinal arteries. In this manner 

 an anterior longitudinal anastomotic chain is formed, which 

 descends for some distance on the filum terminale. 



The posterior spinal arteries are two in number, right and left, 

 and each is a branch of the corresponding vertebral artery. Each 

 vessel descends on the side of the cord in two branches, one being 

 in front of, and the other behind, the posterior nerve-roots. These 

 are reinforced by branches from the lateral spinal arteries, and the 

 lateral longitudinal anastomotic chains, formed in this manner, 

 extend over the entire length of the cord. There are thus five 

 longitudinal anastomotic arterial chains in connection with the 

 cord, namely, one anterior, and two lateral on each side, of which 

 one is in front of, and the other behind, the posterior nerve-roots. 

 From these chains branches are freely given to the pia mater, and 

 through it to the cord. 



Veins of the Spinal Column and Spinal Cord — Veins of the 

 Spinal Column. — ^These veins, which form plexuses, are disposed in 

 five sets, namely, (i)' dorsal, (2) veins of the vertebral bodies, 

 (3) anterior intraspinal, (4) posterior intraspinal, and (5) anterior 

 extraspinal. 



The dorsal spinous venous plexus is situated deeply upon the 

 superhcial surface of the neural arches of the vertebrae, under 

 cover of the multifidus spinae muscle. It receives its tributaries 

 from the integument and muscles of the back, and it communicates 

 with the posterior longitudinal intraspinal plexus by branches, 

 which pierce the ligamenta subflava. In the neck the blood is 

 conveyed away from the plexus by veins which open into the 

 vertebral venous plexus around the vertebral artery of each side ; 

 in the thoracic region by veins which join the dorsal branches of 



