968 



THE NERVE SYSTEM 



Processes of the Dura (processus durae matris), The processes of the dura 

 which project into the cavity of the skull are formed by reduplication 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 (Figs. 718 and 719), so named from its sickle-like form, is 

 a strong arched process which descends vertically in the intercerebral fissure 

 between the two hemispheres of the brain. It is narrow in front, where it is 

 attached to the crista galli of the ethmoid bone, and broad behind, where it is 

 connected with the upper surface of the tentorium cerebelli. Its upper margin 

 is convex, and attached to the inner surface of the skull, in the middle line, as 

 far back as the internal occipital protuberance; it contains the superior or great 

 longitudinal sinus (sinus sagittalis superior^). Its lower margin is free, concave, and 



..INTERNAL JUGULAR 

 VEIN 



FIG. 719. Falx cerebri and tentorium cerebelli, left lateral view. (Testut.) 



presents a sharp, curved edge, which contains the falcial or inferior longitudinal 

 sinus (sinus sagittalis inferior). The tentorial or straight sinus (sinus rectus) is 

 formed by the attachment of the falx cerebri to the tentorium cerebelli. 



The tentorium cerebelli (Figs. 718 and 719) is an arched lamina of dura, elevated 

 in the middle and slightly inclined toward the circumference. It intervenes 

 between the upper surface of the cerebellum and the occipital lobes of the cerebrum. 

 It is attached, behind, by its convex border to the transverse ridges upon the inner 

 surface of the occipital bone, and there encloses on each side the transverse or 

 lateral sinus (sinus transversus); frontad, to the superior margin of the petrous por- 

 tion of the temporal bone on either side, there enclosing the superpetrosal sinus 

 (sinus petrosus superior}; and at the apex of this bone the free or internal border 

 and the attached or external border meet, and, crossing one another, are continued 

 forward, to be attached to the anterior and posterior clinoid processes respectively 



