CHAPTER VI 



THE SPINAL CORD 



THE spinal cord, or medulla spinalis, is a cylindric mass of nervous tissue 

 occupying the vertebral canal. It is 40 to 45 cm. in length, reaching from the 

 foramen magnum, where it is continuous with the medulla oblongata, to the 

 level of the first or second lumbar vertebra. Even above this level the vertebral 

 canal is by no means fully occupied by the cord (Fig. 48), which, as shown in 

 Fig' 49, is surrounded by protective membranes, while between these and the 

 wall of the canal is a rather thick cushion of adipose tissue containing a plexus 



Extradural fat and venous plexus 



Subarachnoid space 

 Spinal nerve roots 



Spinal cord 



Dura mater 



Ligamentum denticulatum 



Fig. 48. Diagram showing the relation of the spinal cord to the vertebral column. 



of veins. Immediately surrounding the cord and adherent to it is the delicate, 

 highly vascular pia mater. This is separated from the thick, fibrous dura mater 

 by a membrane having the tenuity of a spider web, the arachnoid, which sur- 

 rounds the subarachnoid space. This space is broken up by subarachnoid 

 trabeculae and filled with cerebrospinal fluid. 



External Form. The spinal cord is not a perfect cylinder, but is somewhat 

 flattened ventrodorsally, especially in the cervical region. Its diameter is not 

 uniform throughout, being less in the thoracic than in the cervical and lumbar 

 portions. That is to say, the cord presents two swellings (Fig. 51). The cer- 

 vical enlargement (intumescentia cervicalis) comprises all that portion of the cord 



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