THE NERVOUS SYSTEM 



1309 



Doia Mater (Theca) 



Strnetnre. — The spinal dura mater consists of fibrous tissue and some 

 elastic tissue disposed in parallel longitudinal bundles. Its internal and 

 external surfaces are covered by endothelial ceUs. 



Subdural Space. — Between the spinal dura mater and the arach- 

 noid there is a narrow cleft-Hke interv^al, which is known as the 

 subdural space {cavum suhdurale B.). It contains a small amount 

 of fluid, and it communicates freely with the lymph-spaces or clefts 

 in the sheaths of the spinal nerves. It has, however, no communi- 

 cation with the subarachnoid space. 



Spinal Arachnoid Membrane.— This is a delicate transparent 

 membrane which loosely surrounds the spinal cord between the 

 theca externally and 

 the pia mater intern- 

 ally. It is separated 

 from the theca by the /L^\ 

 subdural space, and ^^ 

 from the pia mater ) 

 by the subarachnoid 

 space. Superiorly it 

 is continuous with the 

 cranial arachnoid, and 

 inferiorly it encloses 

 the Cauda equina. On 

 either side it forms 

 sheaths for the pro- 

 cesses of the ligamen- 

 tum denticulatum as 

 far as the inner sur- 

 face of the theca . The 

 ventral and dorsal 

 roots of the spinal 

 nerves also receive 

 sheaths from it, which 

 accompany them 

 through the openir^s 

 in the theca, but soon 

 cease. 



Subarachnoid Space 

 {Cavum Subarachnoi- 



dale B.). — ^This space, which is wide, is situated, as stated, between 

 the arachnoid and pia mater. It contains cerebro-spinal fluid, and 

 its dorsal part is continuous superiorly with the cistema magna of 

 the cranial subarachnoid space, which communicates with the 

 fourth ventricle by three openings (foramen of Magendie and fora- 

 mina of Luschka). 



The subarachnoid space is partially divided into t\^^ compart- 

 ments, ventral and dorsal, by ligamenta subflava, which form in- 

 complete lateral septa. The ventral roots of the spinal nerves 

 traverse the ventral compartment, and the dorsal roots traverse the 



^ Arachnoid 



- -T— Ligamentum Dentictilatum 



Anteiior Nerve-Root 

 Posterior Nerre-Root 

 Pia Mater 



Sinnal Cord 



Anterior Nerve-Root (cot) 



OF THE 



Fig. 545. — Portion 



SHOWING THE Membranes, 

 Dexticul.\ta, and Roots of 

 Nerves. 



Spinal Cord, 



Ligamenta 



THE Spinal 



