THE D URA OF THE BRAIN 



967 



of the bones, the adhesion being most marked opposite the sutures and at the base 

 of the skull. Its inner surface is smooth and lined by a layer of endothelium. 

 It sends inward four processes which divide the cavity of the skull into a series 

 of freely communicating compartments, for the lodgement and protection of the 

 different parts of the brain; and it is prolonged to the outer surface of the skull, 

 through the various foramina which 

 exist at the base, and thus becomes 

 continuous with the pericranium; its 

 fibrous layer forms sheaths for the 

 nerves which pass through these aper- 

 tures. At the base of the skull it 

 sends a fibrous prolongation into the 

 foramen cecum; it sends a series of 

 tubular prolongations around the fila- 

 ments of the olfactory nerves as they 

 pass through the cribriform plate, and 

 another around the nasal nerve as it passes through the nasal slit; a prolongation 

 is also continued through the sphenoidal fissure into the orbit, and another is 

 carried into the same cavity through the optic foramen, forming a sheath for the 

 optic nerve, which is continued as far as the eyeball. In the posterior fossa it 



CNDOSTEAL 



LAYER 



MENINGEAL 



LAYER 



ENDOTHELIAL 



LINING 



FIG. 717. The structure of the dura. Section through 

 r a child, slightly enlarged. (Poirier 



DIAPHRAGMA SELLAE 



ANTERIOR 



CLINOID 



PROCESS 



TENTORIUM 



FIG. 718. The tentorium cerebelli. (Poirier and Charpy.) 



sends a process into the internal auditory meatus, ensheathing the facial and 

 auditory nerves; another through the jugular foramen, forming a sheath for the 

 structures which pass through this Opening; and a third through the anterior con- 

 dylar foramen. Around the margin of the foramen magnum it is closely adherent 

 to the bone, and is continuous with the spinal dura. 



