8 4 



HEAD AND NECK 



below. Its lateral margin is widely serrated or denticulated. 

 From twenty to twenty-two denticulations may be recognised ; 

 the highest is attached to the margin of the foramen 

 magnum. They occur in the intervals between the 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 com- 

 partment. In the 



Posterior. JHBS^I^Kl.. Anterior anterior compart- 



ment the anterior 



Ligamentum 

 denticulatum 



nerve-root 



FIG. 22. Lateral view of the Medulla Spinalis, 

 Dura Mater, and Ligamentum Denticulatum. 

 (Hirschfeld and Leveille".) 



nerve-roots pass 

 laterally ; the pos- 

 terior compartment 

 contains the pos- 

 terior nerve - roots, 

 and is imperfectly 

 subdivided into two 

 lateral subdivisions 

 by the septum sub- 

 arachnoideale. 



Medulla Spinalis 

 (O.T. Spinal Cord). 

 The spinal 

 medulla itself may now be studied in situ. It is almost cylin- 

 drical in form but is slightly flattened anteriorly and pos- 

 teriorly. It extends from the foramen magnum, where it is 

 continuous with the medulla oblongata of the brain, to the 

 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 the conus a slender filament, 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. j in the male it is 45 cm. (18 inches). 



Throughout the greater part of the thoracic region, 

 the medulla spinalis presents a uniform girth, but in the 

 cervical and lower thoracic regions it shows marked swellings, 



