228 CLINICAL APPLIED ANATOMY. 



by a layer of fatty tissue and a considerable venous plexus. The 

 former tissue may give rise to lipomatous growths or be the seat 

 of hydatid disease, or diffuse suppuration, and the veins may be 

 torn in injuries to the spinal column leading to considerable 

 extravasation of blood. The thickening of the dura mater which 

 is known as pachymeningitis may produce pressure on the cord ; 

 hydatids and new growths may be found inside the dura mater 

 and a sudden effusion of fluid into the membranes, the result of 

 haemorrhage or of rupture of an abscess will also produce pressure 

 symptoms. 



The intervertebral foramina afford channels by which new 

 growths, abscesses or even hydatids may invade the spinal canal 

 from without. The close relation of the aorta to the bodies of 

 the vertebrae explains the ease with which aneurysms of the 

 descending thoracic and abdominal portions of the vessel erode 

 the walls of the canal and ultimately exert pressure on the 

 structures contained in it. 



The retroperitoneal glands are favourably placed for invasion 

 of the spinal column and spinal canal when the site of malignant 

 disease, whilst the thoracic part of the spine is often the seat of 

 new growth secondary to carcinoma of the breast. 



Tumours within the dura, being confined by that membrane, 

 more easily produce compression than do tumours outside it. 



Since the spinal nerve roots cross the subdural space and 

 traverse the dura to escape through the intervertebral foramina 

 it is not surprising that pain should be referred to the sensory 

 roots at the level of compression (Figs. 20 23, p. 226). This 

 is most marked in connexion with new growths, especially those 

 which arise in the spinal membranes, and the pain may persist 

 after the skin supplied by the particular nerve roots has become 

 anaesthetic. Root pain is not such a marked feature in compres- 

 sion by aneurysm or caries. Since the anterior spinal roots are 

 motor in function, pressure on these may produce muscular 

 spasm of the muscles which they supply, but more commonly 

 the muscles simply waste. 



The wasting is easily recognised when it occurs in the muscles 



