THE yEINS. 325 



thence proceeds caudoventrad obliquely over the surface of the 

 cerebellum, unites with veins from the ventral side of the 

 brain, leaves the skull by the jugular foramen, forming thus 

 the inferior cerebral vein, and joins the internal jugular vein. 



On the ventral side of the brain are the following sinuses of 

 the dura mater: 



3. Sinus cavernosus. — A short broad venous sinus, one 

 on each side of the hypophysis, on the body of the sphenoid. 

 It receives veins from the side and ventral surface of the brain. 

 The two sinuses are connected by communicating branches 

 craniad and caudad of the hypophysis. From them branches 

 pass out through the orbital fissure to join the plexus formed 

 by the branches of the posterior facial vein. 



4. Sinus petrosus inferior. — This arises from the sinus 

 cavernosus and passes caudolaterad in the groove between the 

 edge of the petrous bone and the basilar portion of the occipi- 

 tal. Reaching the jugular foramen it divides; part joins the 

 termination of the sinus transversus to form the inferior cere- 

 bral vein, which passes through the jugular foramen to join the 

 internal jugular vein. The other portion of the sinus petrosus 

 inferior passes through the condyloid canal of the occipital 

 bone, communicates by a strong transverse branch across the 

 surface of the basioccipital with the vein of the opposite side, 

 and enters the spinal canal through the foramen magnum. 

 Here it joins the sinus of the vertebral column. 



5. Sinus columnas vertebralis. — On the ventral surface of 

 the vertebral canal, beneath the periosteum, are two wide 

 venous sinuses, one on each side of the middle line. These 

 sinuses extend the entire length of the spinal cord. At the 

 atlantal foramen each sends a strong branch to the internal 

 jugular vein. Farther caudad they send branches to the verte- 

 bral, intercostal, and lumbar veins, and Communicate with each 

 other by numerous transverse branches. They receive many 

 small veins from the spinal cord. 



3. Vena cava inferior (Fig. 129, c\ Fig. 126, a). 



The inferior vena cava (Fig. 126, a) is formed at about the 

 level of the last lumbar vertebra by the union of the two common 



