i88 



HEAD AND NECK 



L.V.I. . 



breadth (13 to 14 mm.) opposite the fifth or sixth cervical 

 vertebra. Below, it subsides opposite the second thoracic 

 vertebra. The lumbar swelling begins at the level of the tenth 

 thoracic vertebra, and attains its maximum transverse diameter 

 (n to 13 mm.) opposite the last thoracic vertebra. Below, it 



rapidly tapers into the 

 conus medullaris. 



Filum Terminale. 

 This delicate thread-like 

 filament lies amidst the 

 numerous long nerve-roots 

 which occupy the lower 

 part of the vertebral canal, 

 but it can readily be de- 

 tected from these (i) by 

 its silvery glistening ap- 

 -Nerve-roots pearance, and (2) by its 

 continuity with the ex- 

 tremity of the conus 



S.V.I. 



Conus 

 medullaris 



Filum 



:erminale 



internum 



of tube of 

 dura mater 



Filum 



terminale 



externum 



Coccyx 



Dura mater 



Although the central 

 canal of the medulla 

 Lower end spinalis is prolonged 

 down in its interior 

 for nearly half its 

 length, and nervous 

 elements can be 

 traced in its sub- 

 stance for a like 

 distance, the filum 

 terminale is chiefly 

 composed of pia 

 mater. The linea 

 FIG. 76- Sagittal section through the lower part s pl en dens and the 

 of the Vertebral Canal. , r 



lower ends of the 



ligamenta denticulata may also be considered to be continued 

 into it. At the level of the second or third sacral vertebra 

 it pierces the tapered end of the tube of dura mater, and 

 receives an investment from it ; and, finally, reaching the lower 

 end of the sacral canal, it terminates by blending with the 

 periosteum on the dorsal surface of the coccyx or the last 

 piece of the sacrum. 



