338 SINUSES OF THE DURA MATER. 



veins into the osseous canals in which they are lodged. At the middle 

 period of life these sinuses are confined to the particular bones ; but in old 

 age, after the ossification of the sutures, they may be traced from one bone 

 to the next. They receive their blood from the capillaries supplying the 

 cellular structure of the diploe, and terminate externally in the veins of the 

 pericranium, and internally in the veins and sinuses of the dura mater. 

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

 of medulla. 



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 arranged into the superficial, 

 and deep or ventricular veins. 



The Superficial cerebral veins are situated on the surface of the hemi- 

 spheres, 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 longitudinal 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 ventricles by 

 the veins of the corpora striata and those of the choroid plexus, \vhich unite 

 to form the two venae Galeni. 



The Vena Galeni pass backwards in the structure of the velum interpo- 

 situm ; 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 internal coat 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, 

 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 tuberosity of the occi- 

 pital 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 from the diploe, and near the posterior 



