VENOUS SINUSES OF CRANIUM. 511 



brain (cerebellum) and the posterior part of the large brain (cere- 

 brum). 



Its upper surface is raised along the middle, where it is joined surfaces, 

 by the falx cerebri, and is sloped laterally for the support of the back 

 part of the cerebral hemispheres. Its under surface rests on the 

 small brain, and is joined by the falx cerebelli. 



The anterior concave margin is free, except at the ends where it edges, 

 i> fixed by a narrow slip to each anterior clinoid process. The 

 posterior or convex edge is connected to the following bones : 

 the occipital (transverse groove), the posterior inferior angle of the 

 parietal, the petrous portion of the temporal (upper border), and the 

 posterior clinoid process of the sphenoid. 



Along the centre of the tentorium is the straight sinus ; and in a p d the . 

 the attached edge are the lateral and superior petrosal sinuses on 

 each side. 



The falx cerebelli has a corresponding position below the ten- Falx 

 torium to the falx cerebri above that fold. It is much smaller ** 

 than the falx of the cerebrum, and will appear on detaching the 

 tentorium. Triangular in form, this fold is adherent to the 

 internal occipital crest, and projects between the hemispheres of 

 the small brain. Its base is directed to the tentorium ; and the contains 

 apex reaches the foramen magnum, on each side of which it gives Snus^ 

 a small slip. In it is contained the occipital sinus. 



The SINUSES are channels for venous blood between the layers of Sinuses of 

 the dura mater. They are arranged in two groups, the one com- the skuU ' 

 prising the sinuses that converge towards the internal occipital 

 protuberance, while the other is formed by the cavernous sinuses 

 on the sides of the body of the sphenoid bone and the canals opening 

 into these. 



A. The superior longitudinal sinus has been described at p. 508. Superior 



The INFERIOR LONGITUDINAL SINUS (fig. 187, c) resembles a small and 

 vein, and is contained in the lower border of the falx cerebri at 

 the posterior part. It receives blood from the falx and the 

 large brain, and ends in the straight sinus (d) at the edge of the 

 tentorium. 



The STRAIGHT SINUS (fig. 187, d) lies along the junction of the straight 

 falx with the tentorium, extending from the termination of the S1DUS- 

 preceding sinus to the internal occipital protuberance, where it is 

 continued into one of the lateral sinuses, generally the left. Its form 

 is triangular, like the superior longitudinal. Joining it are the 

 inferior longitudinal sinus, the veins of Galen (which will be seen to 

 be cut or torn oft'short) from the interior of the cerebral hemispheres, 

 and some small veins from the upper surface of the cerebellum. 



The OCCIPITAL SINUS (fig. 187, g) is a small canal in the falx Occipital 

 cerebelli, which reaches from the torcular Herophili to the foramen smus ' 

 magnum and collects the blood from the lower occipital fossae. 

 This sinus may be double. 



The LATERAL SINUSES, right and left, are the channels by which Lateral 

 most of the blood passes from the skull. Each extends from the smuses : 

 internal occipital protuberance, along the winding groove on the 



