THE VEINS OF THE CRANIUM VERTEBRAL AND SPINAL VEINS 689 



loid fossa; it communicates with the condyloid vein issuing from the hypoglossal 

 foramen and is drained by the ventral cerebral vein; it also receives an emissary 

 vein from the temporal canal. The sinus communicates with the cavernous sinus 

 by an oval opening at the carotid notch which transmits the internal carotid artery; 

 the latter forms the first bend of its S-shaped curve in the petrosal and the second 

 in the cavernous sinus. 



The basilar plexus (Plexus basilaris) is situated on the cerebral surface of the 

 basilar part of the occipital bone, and is directly continuous behind with the venous 

 plexus in the atlas. Its chief emissary is the condyloid vein, which brings it into 

 communication with the ventral petrosal sinus. It is connected with the cav- 

 ernous and intercavernous sinuses by small veins. 



The Veins of the Cranium 



The cerebral veins (Venae cerebri) do not in general accompany the cerebral 

 arteries. They have very thin walls, no muscular coat, and no valves. They are 

 arranged in two sets, superficial or cortical and deep or central. The superficial 

 veins are more nmnerous and larger than the arteries. They lie on the surface of 

 the brain in the pia mater and the subarachnoid space. 



The ascending cerebral veins drain most of the convex surface and the medial 

 surface of the cerebral hemispheres. Most of them open into the dorsal longitudi- 

 nal sinus, but some enter the confluens sinuum or the transverse sinuses. Near the 

 termination they become bulbous, and open into the sinus obliquely and in such a 

 manner as to tend to prevent reflux of blood into them.^ The descending cerebral 

 veins which come chiefly from the ventral part of the convex surface of the cere- 

 brum open into the vena rhinalis posterior. 



The basal cerebral veins converge to a large common trunk, the vena rhinalis 

 posterior; this begins at the anterior end of the piriform lobe, runs backward in a 

 groove on the latter, enters the tentorium cerebelli, and opens into the dorsal 

 petrosal sinus. 



The deep cerebral veins issue from the central or ganglionic parts of the brain 

 at the transverse fissure. The principal ones come from the chorioid plexuses, the 

 corpus striatum, and the septum pellucidum. These unite to form the internal 

 cerebral veins (Vv. cerebri internae), which run backward in the roof of the third 

 ventricle and unite to form the great cerebral vein (V. magna cerebri). This 

 passes upward and backward behind the splenium of the corpus callosum and is 

 continued as the straight sinus to join the longitudinal sinus. 



The dorsal cerebellar veins ramify on the upper surface of the cerebellum. 

 They go chiefly to the occipital and dorsal petrosal sinuses. The ventral cerebellar 

 veins are larger and go chiefly to the basilar plexus. The veins of the medulla and 

 pons end chiefly in the basilar plexus and the occipital and dorsal (and accessory) 

 petrosal sinuses. 



The meningeal veins (^^en£e meningese) arise in capillary plexuses in the su- 

 perficial and deep faces of the dura mater. Some end in the sinuses of the dura, 

 others accompany the meningeal arteries. 



The diploic veins (Venje diploicse) are anastomosing channels in the spongy 

 substance of the cranial bones. Their walls are thin, consisting in many places 

 only of the endothelium, and they have no valves. Some open inward into venous 

 sinuses, others into extracranial veins. 



Vertebral and Spinal Veins 

 Two venous trunks, the longitudinal vertebral sinuses (Sinus vertebrales 

 longitudinales), extend along the floor of the vertebral canal, one on either side of 



1 Most of these veins open into the sinus in the direction of the blood-stream in the sinus, but 

 some of the posterior ones open about at a right angle, or even contrary to the direction of the cur- 

 rent. 



44 



