THE DISSECTION OF THE BACK 



187 



spinal nerves, and, pushing the arachnoid before them, they 

 are attached by their pointed extremities to the inner surface 

 of the dura mater. 



The ligamenta denticulata maintain the medulla spinalis 

 (O.T. spinal cord) in the middle of the tube of dura mater and 

 partially subdivide the sub-arachnoid space into an anterior 

 and a posterior compartment. In the anterior compartment 

 the anterior nerve-roots pass laterally ; the posterior compart- 

 ment contains the posterior nerve-roots, and is imperfectly 

 subdivided into two lateral subdivisions by the septum 

 posticum. 



Medulla Spinalis 

 (O.T. Spinal Cord). 

 The spinal medulla 

 itself may now be 

 studied in situ. It is 

 a cylindrical structure, 

 slightly flattened an- 

 teriorly and pos- 

 teriorly, which extends 

 from the foramen 

 magnum, where it is 

 continuous with the 

 medulla oblongata of 

 the brain, to the 



Ligament 

 denticulatum 



FIG. 75. Lateral view of the Medulla Spinalis, 

 Dura Mater, and Ligamentum Denticulatum. 

 (Hirschfeld and Leveille".) 



lower border of the 

 body of the first or 

 the upper border of the body of the second lumbar vertebra. 

 Its lower end rapidly tapers to a point, and is termed the 

 conus medullaris. From the extremity of this, a slender fila- 

 ment, termed the filum terminate, is prolonged downwards to 

 the dorsal surface of -the coccyx. 



In the female the average length of the medulla spinalis is 

 43 cm. ; in the male it is 45 cm. 



Throughout the greater part of the thoracic region of the 

 spine the medulla spinalis presents a uniform girth, but in the 

 cervical and lower thoracic regions it shows marked swellings, 

 termed respectively the intumescentia cervicalis and intumescentia 

 lumbalis. From these enlargements proceed the nerves which 

 supply the upper and lower limbs. The cervical swelling is the 

 more evident of the two. It begins at the upper end of the 

 medulla spinalis (O.T. spinal cord) and attains its greatest 



