THE SPINAL CORD. 



303 



)Nsl 



cerebellum presents a great num- 

 ber of fissures. One, the great 

 horizontal fissure, is of large size, 

 and divides the cerebellum into 

 an upper and lower portion. If 

 a vertical section is made through 

 the cerebellum, a remarkable ar- 

 rangement of the gray cortical 

 matter into laminae is observed. 

 It is called the arbor vitae cere- 

 belli. 



THE SPINAL CORD. 



The spinal cord is that por- 

 tion of the cerebro-spinal system 

 situated in the spinal canal. It 

 is invested by three membranes, 

 the dura mater, the arachnoid, 

 and the pia mater. The dura 

 mater of the cord differs from 

 the dura mater of the brain, 

 firstly, in that it is a loose, tubu- 

 lar sac which is not adherent to 

 the bones of the spinal canal ; 

 secondly, it does not send proc- 

 esses into the cord; and, thirdly, 

 its lamellae do not diverge to form 

 blood-sinuses. It is attached to 

 the margins of the foramen mag- 

 num, and forms tubular sheaths 

 for the anterior and posterior 

 roots of spinal nerves. Its lower 

 end becomes blended with the 

 periosteum of the sacrum and 

 coccyx. 



The arachnoid, as in the 



