370 SINUSES OF THE DURA MATER. 



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 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 in- 

 ferior, 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, 

 which unite to form the two venae Galeni. 



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

 terpositum ; 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 OP 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. 



