868 



HUMAN ANATOMY. 



the occipital. From this meeting-point, which is termed the torcular Herophili (con- 

 fluens sinuum), each lateral sinus passes outward over the squamous portion of the 

 occipital bone along the line of the attachment of the tentorium cerebelli, and, passing 

 over the posterior inferior angle of the parietal, is continued inward upon the inner 

 surface of the mastoid portion of the temporal and the jugular process of the occipital 

 to reach the jugular foramen, where it opens into the internal jugular vein. As it passes 

 upon the mastoid portion of the temporal, it leaves the line of attachment of the ten- 

 torium cerebelli, passing somewhat downward as well as inward, and follows the line 

 of junction of the petrous and mastoid portions of the bone in a somewhat S-shaped 

 course, whence this portion of it is frequently termed the sigmoid sinus. 



A difference in size is usually noticeable in the sinuses of the opposite sides, 

 that of the right being usually the larger, and this difference is due to the mode in 

 which the various sinuses meet at the torcular Herophili. Most frequently the 

 superior longitudinal sinus communicates mainly with the right lateral, while the 



Fig. 755. 



Skin 



Superior longitudinal sinus 



Falx cerebri 



Cerebral 

 hemisphere i 



Posterior horn of 

 lateral ventricle 



Tentorium 



Left lateral sinus 



Superior worm 



Fibro-aponeurotic layers of scalp 

 Parietal layer of dura 

 Bone 



Inferior longitudi- 

 nal sinus, cut 

 obliquely 



Posterior horn of 

 lateral ventricle 



Pentorium 



Right lateral sinus 



Cerebellum 



Inferior worm 



Occipital sinus 



Frontal section of head, viewed from behind, showing relations of dura mater to sinuses 

 and to cerebral hemispheres and cerebellum. 



Straight sinus opens principally into the left, the greater amount of blood carried by 

 the superior longitudinal, as compared with that transmitted by the straight, resulting 

 in the larger size of the right lateral sinus. Indeed, in some cases the right lateral 

 sinus is practically the direct continuation of the superior longitudinal and the left 

 lateral of the straight, the two laterals being connected only by a short and relatively 

 small connecting arm, which represents the torcular Herophili. Throughout that 

 portion of their courses in which the lateral sinuses lie in the line of attachment of the 

 tentorium cerebelli they are triangular in cross-section (Fig. 755), but in their mastoid 

 (sigmoid) portion they are semi-circular ; the right sinus has a diameter of from 

 9-12 mm., while the left varies from 3-5 mm. At the jugular foramen each sinus 

 makes a sudden bend and opens either directly into the summit of the superior jugular 

 bulb, or else at a varying distance downward upon the anterior surface of the bulb, 

 the upper extremity of which then forms a dome-shaped structure projecting upward 

 into the jugular foramen. 



