CEREBRAL AND CEREBELLAR VEINS. 331 



veins are separated from the bony walls of the canals by a thin 

 layer of marrow. 



CEREBRAL AND CEREBELLAR VEINS. 







The cerebral veins are remarkable for the absence of valves, and 

 for the extreme tenuity of their coats. They may be divided into 

 the superficial, and deep or ventricular veins. 



The Superficial cerebral veins are situated upon the surface of the 

 hemispheres, lying in the grooves formed by the convexities of the 

 convolutions. They are named from the position which they may 

 chance to occupy upon the surface of this organ, either superior or 

 inferior, internal or external, anterior or posterior. 



The Superior cerebral veins, seven or eight in number on each 

 side', pass obliquely forwards, and terminate in the superior longitu- 

 dinal sinus, in the opposite direction to the course of the stream of 

 blood in the sinus. 



The Deep or Ventricular veins commence within the lateral ven- 

 tricles by two vessels, the vena corporis slriati and the veins of the 

 choroid plexus, which unite to form the two vena? Galeni. 



The Venae, Galeni pass backwards in the structure of the velum 

 interpositum ; and escaping through the fissure of Bichat, terminate 

 in the straight sinus. 



The Cerebellar veins are disposed, like those of the cerebrum, on 

 the surface of the lobes of the cerebellum ; they are situated some 

 upon the superior, and some upon the inferior surface, while others 

 occupy the borders of the organ. They terminate in the lateral 

 and petrosal sinuses. 



SINUSES OF THE DURA MATER. 



The sinuses of the dura mater are irregular channels, formed by 

 the splitting of the layers of that membrane, and lined upon their 

 inner surface by a continuation of the serous layer of the veins. 

 They may be divided into two groups: 1. Those situated at the 

 upper and back part of the skull. 2. The sinuses at the base of the 

 skull. The former are, the 



Superior longitudinal sinus, 

 Inferior longitudinal- sinus, 

 Straight sinus, or sinus quartus, 

 Occipital sinuses, 

 Lateral sinuses. 



The Superior longitudinal sinus, is situated in the attached margin 

 of the falx cerebri, and extends along the middle line of the arch of 

 the skull, from the foramen caecum in the frontal, to the inner tube- 

 rosity of the occipital bone, where it divides into the two lateral 

 sinuses. It is triangular in form, is small in front, and increases 

 gradually in size as it passes backwards ; it receives the superior 

 cerebral veins which open into it obliquely, numerous small veins 



