INTRASPIXAL VESSELS. 



549 



tlie surface. Three larger processes of the pia mater extend into 

 the back of the cord ; these are the posterior median septum already 

 referred to, and the posterior intermediate septum on each side, seen 

 only in the cervical region, which passes forwards from the furrow 

 of the same name, and separates the posterior median and postero- 

 external columns. 



Modifications in the qrey and ivhite substance. The white substance Grey and 

 . ... i -i j j i white sub- 



miicli exceeds the grey in quantity in the cervical and dorsal stance vary. 



regions ; but it is less abundant in proportion to the grey matter 

 in the lumbar enlargement. The grey substance is least in amount 



FIG. 200. IXTRASPIXAL ARTERIES 

 ix THK LOINS. 



a. Branch of a lumbar artery. 



b. Ascending, and c, descending 

 offset. 



d. Offset to the body of the 

 vertebra on each side. 



e. Central artery formed by offsets 

 from the lateral loops. 



FIG. 201. INTRASPIXAL VEINS 

 IN THE LOINS. 



a. Branch to join a lumbar 

 vein. 



b. Anterior longitudinal vein, 

 one on each side. 



c. Veins from the bodies of 

 the vertebrae. 



in the dorsal region ; the anterior horn is specially large in the 

 cervical region, and in the lumbar enlargement both horns are 

 large and the grey matter forms a considerable proportion of the 

 substance of the cord. The posterior horn is massive, though not 

 quite so large as the anterior. 



The cornua of the grey crescents decrease in length from above 

 down, especially the posterior, and towards the end of the cord they 

 blend in one indented or cruciform mas.-. 



IXTRASPIXAL VESSELS. Arteries supply the cord and its mem- 

 branes, and the bodies of the vertebrae. The veins form a remark- 

 aide plexus within the canal, but this will not be seen unless they 

 have been specially injected. 



The intraspinal arteries (fig. 200, a) are derived from the vessels 

 along the sides and front of the spinal column, viz., from the 

 vertebral and ascending cervical in the neck, from the intercostal in 



Crescents 

 alter their 

 shape. 



Vessels of 

 the spinal 

 canal. 



Source of 

 the intra- 

 spinal 

 arteries. 



