542 



VEINS. 



SINUSES OF THE DURA MATER. 



The Sinuses of the Dura Mater are venous channels, analogous to the veins, 

 their outer coat being formed by the dura mater; their inner, by a continuation 

 of the serous membrane of the veins. They are fifteen in number, and are 

 divided into two sets. 1. Those situated at the upper and back part of the skull. 

 2. Those at the base of the skull. The former are the 



Superior longitudinal. 

 Inferior longitudinal. 



Straight sinus. 

 Lateral sinuses. 



Occipital sinuses. 



The Superior Longitudinal /Sinus occupies the attached margin of the falx 

 cerebri. Commencing at the crista Galli, it runs from before backwards, 



Fig. 305. Vertical Section of the Skull, showing the Sinuses of the Dura Mater. 



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grooving the inner surface of the frontal, the adjacent margins of the two 

 parietal, and the superior division of the crucial ridge of the occipital bone, 

 and terminates by dividing into the two lateral sinuses. This sinus is triangular 

 in form, narrow in front, and gradually increasing in size as it- passes back- 

 wards. On examining its inner surface, it presents the internal openings of the 

 cerebral veins, which run, for the most part, from behind forwards, and open 

 chiefly at the back part of the sinus, their orifices being concealed by fibrous 

 areolse ; numerous fibrous bands (chordse Wiliisii) are also seen, which extend 

 transversely across the inferior angle of the sinus ; and lastly, some small, white, 

 projecting bodies, the glandulae Pacchioni. This sinus receives the superior 

 cerebral veins, numerous veins from the diploe and dura mater, and, at the 

 posterior extremity of the sagittal suture, the parietal veins from the peri- 

 cranium. 



The point where the superior longitudinal and lateral sinuses are continuous 

 is called the confluence of the sinuses, or the torcular Herophili. It presents a 

 considerable dilatation, of very irregular form, and is the point of meeting of 

 six sinuses, the superior longitudinal, the two lateral, the two occipital, and the 

 straight. 



The Inferior Longitudinal Sinus, more correctly described as the inferior longi- 

 tudinal vein, is contained in the posterior part of the free margin of the falx 

 cerebri. It is of a circular form, increases in size as it passes backwards, and 



