164 



TOPOGRAPHICAL ANATOMY OF THE 



bundles of fibres forming the roots of the spiual nerves pierce the wall 

 of the tube, and in doing so derive a thin fibrous sheath therefrom. 



Dissection. — The dura mater must now be carefully slit along the 

 middle line. This havin<;- Ijeeu done, the smooth nature of its interior 

 will be manifest. The interval between the dura mater and the arachnoid 

 is known as the subdural i^pace (cavuiu subdurale). 



Pia mater.---^ 

 Arachnoid. — 

 Dura mater. 



Lig. denticulatum., 



>. Dorsal rootlets (cut). 



Arachnoid. \xk 



Lig. denticulatum. \^^ 



^\'entral rootlets. 



N. accessorius (spinal root). 



Spinal ganglion. 



^^ 



"> Dorsal rootlets. 



Pia mater. ---I- y — + 



Spinal cord. 



Fig. 75. — The spinal meninges. The fourth and fifth cervical segments of 

 the spinal cord are illustrated. 



On comparison, it is obvious that marked differences exist between 

 the dura mater covering the brain and its continuation over the spinal 

 cord. The cranial dura mater is closely adherent to, and forms the 

 internal periosteum of, the cranial bones ; the spinal dura mater is 

 separated from the vertebrfe by a space (cavum epidurale) in which 

 there is a certain amount of fatty tissue. The cranial dura mater 

 consists of two layers, from one of which membraoous partitions are 

 formed ; the spinal dura mater corresponds to the inner of these two 

 layers only. Venous sinuses are present in the cranial dura mater; the 

 corresponding membrane of the spinal cord is devoid of them. 



