486 



APPLIED ANATOMY. 



Pons 



spinal just behind the posterior spinal roots (Fig. 489). The veins are more numer- 

 ous They consist of three sets or plexuses, one on the cord m the meshes of the 

 pia mater, another in the spinal canal between the dura mater and the bone, and 

 the third 'on and around the outside of the vertebrae. The veins on the cord 

 in the anterior and posterior median fissures communicate above with the veins 

 of the medulla. The lateral veins empty through the radicular veins which accom- 

 pany the spinal nerve roots. The veins 

 in the spinal canal form anterior and 

 posterior plexuses between the dura 

 and bone and communicate with the 

 extraspinal plexuses around the laminae 

 and spinous processes posteriorly (dorsi- 

 spinal veins) and the plexus around 

 the bodies anteriorly. 



Spinal Hemorrhage. Spinal 

 hemorrhages, though sometimes caused 

 by disease, are usually the result of in- 

 jury. They frequently accompany frac- 

 tures and dislocations. They may be 

 either extradural, intradural, or in the 

 cord haematomyelia. They exist either 

 coincident with the original injury or 

 appear within a few hours. 



Spinal hemorrhages are rarely large 

 and those in the substance of the cord 

 are the more common. They are usu- 

 ally venous. Extradural hemorrhage 

 comes from the plexuses between the 

 dura and bone and the clot may extend 

 through the intervertebral foramina. It 

 is usually of small extent and practically 

 does not produce paralysis from pressure 

 on the cord, hence operation for its 

 relief is useless. Intradural hemorrhage 

 comes from the vessels of the pia and 

 may invade not only the subarachnoid 

 but also the subdural space. It may 

 remain localized at the site of injury 

 or the blood may sink and fill a con- 

 siderable portion of the spinal canal. 

 Owing to the looseness of the cord in its 

 dural sheath the hemorrhage spreads 

 and does not usually give rise to pressure 

 symptoms, hence operation is rarely ad- 

 visable. Large hemorrhage sometimes comes down from cerebral apoplexy or injuries. 

 Hcematomyelia. Hemorrhage into the substance of the cord may be caused by 

 extension or accompany the contusion due to dislocation or fracture. The paralysis 

 which follows serious injuries of the spine is usually due to hemorrhage into the gray 

 or white matter of the cord. The gray matter being the softer is the more frequently 

 affected, the blood penetrating it for quite a distance. Hemorrhage into the gray 

 matter destroys it and produces an incurable paralysis. When into the white matter 

 restoration of function through absorption may occur in from four to six weeks. In 

 either case operation usually is of no service. The location of the hemorrhage will 

 be revealed by the interference with the functions of the cord. The hemorrhage can 

 occur in the form of a column of blood infiltrating the gray matter of several seg- 

 ments in one or both directions from the starting-point. The longer extension is 

 usually toward the brain. It is usually limited to one side of the cord. Generally in 

 small and sometimes in large hemorrhages the effect is mainly mechanical, but espe- 

 cially large hemorrhages may be surrounded by areas of softening. 



Spinal cord, 

 covered with 

 arachnoid 

 and pia 



FIG. 488. Upper part of spinal cord within dural 

 sheath, which has been opened and turned aside; ligamenta 

 denticulata and nerve-roots are shown as they pass out- 

 ward to dura. (Piersol.) 



