THE DURA MATER 



873 



Io the bones, and a membrane for the protection of the brain. It is composed of 

 wo layers, an inner or meningeal and an outer or endosteal, closely connected 

 ogether, except in certain situations, where, as already described (page 654), 

 they separate to form sinuses for the passage of venous blood. Its outer surface 

 is rough and fibrillated, and adheres closely to the inner surfaces of the bones, 

 the adhesions being most marked opposite the sutures and at the base of the skull 



bits 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 communicat- 

 ing 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 peri- 

 cranium; its fibrous layer forms sheaths for the nerves which pass through these 

 apertures. Around the margin of the foramen magnum it is closely adherent to 

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



Great cerebral vein 



Glogsopharynyeal nerve 



Vagus nerce 

 Accessory nerve 



Acoustic nerve 



Facial nerve 



Optic nerves 

 Ophthalmic artery 

 Diaphragma sellce 

 Oculomotor nerves 

 Trochlear nerve 



Abducent nerve Trigeminal nerve 

 Fio. 765. Dura mater and its processes exposed by removing part of the right half of the skull and the brain. 



Processes. The processes of the cranial dura mater, which projects into the 

 cavity of the skull, are formed by reduplications of the inner or meningeal layer 

 of the membrane, and are four in number: the falx cerebri, the tentorium cerebelli, 

 the falx cerebelli, and the diaphragma sellae. 



The falx cerebri (Fig. 765), so named from its sickle-like form, is a strong, arched 

 process which descends vertically in the longitudinal fissure between the cerebral 

 hemispheres. It is narrow in front, where it is attached to the crista galli of the 

 ethmoid; and broad behind, where it is connected with the upper surface of the 





