34 A MANUAL OF ANATOMY. 



left between the two layers of the dura called the cranial 

 sinuses. These sinuses are also found at other points than 

 where these processes are given off, as at the base of the 

 skull. The sinuses will follow later ; see below. 



DISSECTION. 



Split open the superior longitudinal sinus from its beginning to its ending, 

 and in doing so notice the cords which cross it. These are the chordae 

 Willisii. 



Divide the dura, just above the bone, entirely around the head. Raise the 

 dura from the brain and turn it upward at the sides as far as possible ; this 

 will expose the attachment of the falx cerebri. 



The falx is to be cut from its attachment, and with the dura turned back- 

 ward. Divide the cerebral veins when encountered, and turn the dura off 

 backward from the brain, exposing its upper surface. As a rule the dura is 

 not removed far enough backward. 



In the free margin of the falx will be seen a very small opening, looking 

 like a slit. This is the inferior longitudinal sinus. 



The Falx Cerebri. Figs. 8 and 9. 



This is a sickle-shaped process of the dura which lies 

 between the two cerebral hemispheres. It is attached all 

 along its base to the dura (with which it is continuous) and 

 at its attachment, by the divergence of its layers is formed 

 the superior longitudinal sinus. See below. Its anterior 

 extremity is fastened to the crista galli, and its posterior 

 extremity to the upper surface of the tentorium cerebelli. 

 At this rear attachment the straight sinus is formed by the 

 separation of its layers, similar to the formation of the su- 

 perior sinus. 



The Superior Longitudinal Sinus. Diag. i. Fig. 8. 



As stated above, this sinus is formed at the base of the 

 falx cerebri, where its two layers pass off laterally into the 

 inner layer of the dura. 



