Fig' 54- Position of Spinal Cord and Spinal Nerves in the Spinal 



Canal. 



The Skull and tlie Spinal Canal of a female child, a few months old, have 



been opened from behind ; the Dura Mater slit open; and the ribs ivith the 



transverse processes of the vertebrae dissected aid. 



The spinal cord, is, as a whole, very well protected. Anteriorly, it lies 

 at a great distance from the surface of the body; behind, a very thick mass 

 of muscles fills the space between the vertebrae and the prominent spinous pro- 

 cesses (cf. the transverse section through neck, thorax and abdomen). The spinal 

 canal, in which the cord lies, is closed completely in front by the bodies of the 

 Vertebrae and the Intervertebral Discs; behind there is a space between the neural 

 arches through which a knife, dagger or other sharp instrument (e. g. for Lumbar 

 Puncture) may enter. These interlaminar spaces are widest in the cervical region 

 where the neural arches are furthest apart; this explains why the spinal cord is 

 more frequenth' injured h\ sharp weapons in this region than in any other part_ 

 In the upper dorsal region, the neural arches overlap each other and thus almost 

 close the spinal canal posteriorly. In the lumbar region the arches are very broad 

 and thus afford protection to the cord. 



The close relation of the cord to the column accounts for the frequent 

 injury to the C'oril in fractures of the Spinal Column. These fractures are usually 

 indirect, and occur chiefl}' where a comparatively movable portion joins a more 

 fixed ]3ortion; i. e. at the 5th and 6th Cervical and at the 12th Dorsal and ist 

 Lumbar \^ertebrae. 



The Dura Mater does not lie on the wall of the Spinal canal; a cushion, 

 formed by fat, and a large venous plexus lie between the bone and the meninges. 

 Between the Dura Mater and the Cord lies the Arachnoid Sac filled with cerebro- 

 spinal fluid : these arrangements allow the cord to follow the movements of the 

 Column, without friction against the bone. 



As the upper limit of the spinal cord, the upper border of the posterior 

 arch of the Atlas, is usually taken, i. e. the point where the first Cervical Nerve 

 emerges. The cord shews two fusiform enlargements in the regions where the 

 nerves to the extremities leave it. The direction of these enlargements is more 

 in the transverse than in the antero-posterior diameter. The upper or Cervical 

 enlargement is most marked between the 5th and 6th Cervical Vertebrae, the lower 

 or Lumbar is most marked at the nth Dorsal Vertebra. The cord then becomes 

 more slender, ending in the Conus Terminalis which lies at the level of the ist 

 or 2nd Lumbar Vertebra. A filiform continuation of the Conus Terminalis, called 

 the Filum Terminate, runs vertically downwards to the periosteum of the Coccyx. 



The 31 pairs of Spinal Nerves leave the Spinal Canal through the Sub- 

 vertebral Foramina, ensheathed in processes of Dura Mater. This explains wh}' 



