464 



VEINS. 



numerous veins from the diploe and dura mater, and, at the posterior extremity 

 of the sagittal suture, the parietal veins from the pericranium. 



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 con- 

 siderable 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 

 longitudinal 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 

 terminates in the straight sinus. It receives several veins from the falx cerebri, 

 and occasionally a few from the flat surface of the hemispheres. 



The Straight Sinus is situated at the line of junction of the falx cerebri with 

 the tentorium. It is triangular in form, increases in size as it proceeds back- 

 wards, and runs obliquely downwards and backwards from the termination of the 

 inferior longitudinal sinus to the torcular Herophili. Besides the inferior lon- 

 gitudinal sinus, it receives the venae Galeni, the inferior median cerebral veins, 

 and the superior cerebellar. A few transverse bands cross its interior. 



Fig. 238. Vertical Section of the Skull, showing the Sinuses of the Dura Mater. 



'eramtn Caew 



The Lateral /Sinuses are of large size, and situated in the attached margin of 

 the tentorium cerebelli. They commence at the torcular Herophili, and, passing 

 horizontally outwards to the base of the petrous portion of the temporal bone, 

 curve downwards and inwards on each side to reach the jugular foramen, where 

 they terminate in the internal jugular vein. Each sinus rests, in its course, upon 

 the inner surface of the occipital bone, the posterior inferior angle of the parietal, the 

 mastoid portion of the temporal, and on the occipital again just before its termi- 

 nation. These sinuses are of unequal size, the right being the larger, and they 

 increase in size as they proceed from behind forwards. The horizontal portion is 

 of a triangular form, the curved portion semi -cylindrical ; their inner surface is 

 smooth, and not crossed by the fibrous bands found in the other sinuses. These 

 sinuses receive blood from the superior longitudinal, the straight, and the occipital 

 sinuses ; and in front they communicate with the superior and inferior petrosal. 

 They communicate with the veins of the pericranium by means of the mastoid 

 and posterior condyloid veins, and they receive the inferior cerebral and inferior 

 cerebellar veins, and some from the diploe. 



The Occipital are the smallest of the cranial sinuses. They are usually two in 

 rxumber, and situated in the attached margin of the falx cerebelli. They commence 



