THE PIA MATEE. 



675 



lateral part is the chorioidal fissure. This is continuous with the intermediate 

 part, and has already been described in connexion with the inferior horn of the 

 lateral ventricle (p. 636). 



Pia Mater Spinalis. The pia mater of the spinal medulla is thicker and 

 denser than that of the brain. This is largely due to the addition of an outside 

 fibrous layer, in which the fibres run chiefly in the longitudinal direction. The 

 pia mater is very firmly adherent to the surface of the spinal medulla, and in 

 front it sends a fold into the anterior-median fissure of the spinal medulla. The 

 posterior median septum is likewise firmly attached to its deep surface. In front 

 of the anterior-median fissure of the spinal medulla the pia mater is thickened in 

 the form of a longitudinal glistening band, termed the linea splendens, which runs 

 along the whole length of the spinal medulla, and blends with the filum terminale 

 below. The blood-vessels of the spinal medulla lie between the two layers of the 

 pia mater. 



The nerves which leave both the brain and spinal medulla receive closely 



Commissura hippocampi 



Corpus callosum ~~ 

 Nucleus caudatus 



Gyrus cinguli Indusium Stria longitudinalis medialis 



urn septi pellucidi 

 Septum pellucidum 



, - Ventriculus lateralis 

 , Crus fornicis 



Plexus chorioideus 

 lateralis 



~-.~ Stria terminalis 



- Attachment of lamina chorioidea 



Tela chorioidea 



;Q /\ P "^Thalamus (free surface) 



Thalamus / \ Tsenia thalami 



Plexus chorioideus vent, tertii Ventriculus tertius 

 G. 600. DIAGRAM OF A FRONTAL SECTION ACROSS THE CHORIOID TELA OP THE THIRD VENTRICLE. 

 lied sheaths from the pia mater. These blend with the connective- tissue sheaths 

 of the nerves. 



The ligamentum denticulatum is a strong fibrous band which stretches out like 

 a wing from the pia mater on each side of the spinal medulla, so as to connect 

 the pia mater with the dura mater. The pial or medial attachment of the ligament 

 extends in a continuous line between the anterior and posterior nerve-roots, from 

 the level of the foramen magnum above to the level of the first lumbar vertebra 

 below. Its lateral margin is serrated or denticulated, and for the most part free. 

 From twenty to twenty-two denticulations may be recognised. They occur in the 

 intervals between the spinal nerves, and, pushing the arachnoid before them, they 

 are attached by their pointed ends to the inner surface of the dura mater. The 

 ligamenta denticulata partially subdivide the wide subarachnoid space in the 

 vertebral canal into an anterior and a posterior compartment. The anterior 

 nerve -roots traverse the anterior compartment, whilst the posterior nerve- 

 roots traverse the posterior compartment. Further, the posterior compartment 

 is imperfectly subdivided into a right and a left half by the septum posterius. 



By means of the ligamenta denticulata the spinal medulla is suspended in the 

 iddle of the tube of dura mater. 



