546 



THE SPINAL CORD AND ITS MEMBRANES. 



Anterior 

 surface, how 

 known. 



Dissection 

 to see con- 

 stituents of 

 cord. 



Furrows of 

 the cord are 

 anterior 

 median. 



posterior 

 median, 



FIG. 197. MEMBRANES OP THE 

 SPINAL CORD LAID OPEN, TO 



SHOW THE LOWER END OP 



THE CORD WITH THE FlLUM 



TERMINALE. 



a. Dura mater, and b, the 

 fibrous band fixing it to the 

 coccyx. 



c. Pointed lower end of the 

 cord (conus medull.-iris). 



d. Filum terraiuale of the 

 cord. 



of the limbs are attached. There are, 

 therefore, two enlargements on it, viz., 

 cervical or brachial, and lumbar or 

 crural ; the one in the neck reaches 

 from the first cervical to the first 

 dorsal vertebra ; the other is smaller, 

 and is on a level with the eleventh 

 and twelfth dorsal vertebrae. In the 

 upper enlargement the greatest thick- 

 ness is from side to side ; but in 

 the lower swelling the measurement 

 from before backwards nearly equals 

 the transverse. 



While the pia mater remains on the 

 cord, the anterior surface is distin- 

 guished from the posterior by the cen- 

 tral fibrous band and by the anterior 

 spinal arti-ry ; as well as by the 

 irregular line of the anterior nerve- 

 roots, which approach the middle 

 towards the lower end. 



Dissection. For the examination 

 of the structure the student will re- 

 quire a piece of fresh cord which has 

 been hardened in spirit and formalin, 

 since the cord which is obtained 

 from the body at this period is not 

 fitted for the purpose of dissection. 

 Supposing the pia mater with the 

 roots of the nerves removed on one 

 side, the student will be able to 

 observe the following divisions of 

 the cord. 



SULCI OF THE CORD (fig. 198). 



The anterior median fissure occupies 

 the middle line of the front of the 

 cord in its whole length, and pene- 

 trates about one-third of the thickness 

 of it. It is lined by a fold of the 

 pia mater, and is deepest towards 

 the lower end of the cord. White 

 medullary substance bounds the fis- 

 sure ; and at the bottom of it the 

 white fibres are transverse, and are 

 separated by apertures for blood- 

 vessels. 



Along the back of the cord, also in 

 the middle line, there is a narrow 

 groove, from which a process of 

 the pia mater called the posterior 



