Membranes of the Brain and Spinal Cord. 



93 



Jncisura 

 tent or 

 petrosa 

 tempor. 



433. The Processes of the Dura mater. 



The brain and spinal cord are covered by three membranes : the 

 Dura mater (Meninx fibrosa), the Arachnoidea (Meninx serosa) and the Pia 

 mater (Meninx vasculosa). 



The Dura mater forms the external covering; it is a thick and 

 dense inelastic fibrous membrane, whose outer surface adheres closely 

 to the inner surface of the bones, forming their internal periosteum. It 

 sends numerous processes inwards, into the cavity of the skull, and is 

 prolonged to the outer surface of the skull through the various foramina 

 which exist at the base; its fibrous layer forms sheaths for the nerves 

 which pass through these apertures. In certain situations in the skull, 

 the fibrous layers of this membrane separate, to form sinuses for the 

 passages of venous blood, Sinus durae matris. 



The Dura mater also sends inwards into the cavity of the skull 

 three strong membranous processes, the Falx cerebri s. Processus 

 falciformis major, the Falx cerebelli s. Processus falciformis minor, and the 



Tentorium cerebelli. 



13* 



