694 THE VEINS. 



throughout the whole extent of the vertebral column, on the sides of the roof 

 of the spinal canal. Lodged in the lateral depressions on the superior face of 

 the vertebral bodies, at the side of the common superior vertebral ligament, and 

 covered by the dura mater, these reservoirs, continued from one vertebra to the 

 other, are like two large, irregular, parallel veins, which commence at the atlo- 

 axoid articulation, terminate on the first coccygeal vertebrae, where their presence 

 is yet well defined, and communicate with one another during their course by 

 transversal anastomoses (Fig. 386, 3). 



Affluent Veins that open into the Sinuses of the Dura Mater. — 

 These are the vessels which carry blood either from the dura mater itself, or 

 from the substance of the nerve-centres : those of the first category are rare, but 

 the second are numerous. Although we are unwilling to make a detailed study 

 of the latter, we must nevertheless notice what is most remarkable in their 

 disposition. 



a. On the brain, the veins form a much richer and closer network than that 

 of the arterial ramifications ; from this network proceed a certain number of 

 principal branches, which throw themselves into the sinuses of the cranial dura 

 mater. The veins of the cerebrum, for the most part, gain the median and 

 transverse sinuses ; a few only pass into the cavernous sinuses. Those of the 

 medulla oblongata and cerebellum go to the petrosal and occipital sinuses. 



With regard to the internal veins of the brain — those which, by their inter- 

 lacing, constitute the choroid plexus — they unite into a large trunk — the great 

 vein of the brain, or vena Galeni, which bends round the superior extremity of the 

 corpus callosum, reaches the interlobular fissure, and enters the falciform or 

 middle sinus, near its posterior end, after receiving the superficial veins from 

 the inner face of the hemispheres. 



b. The venules arising from the spinal cord are also very remarkable for the 

 fine network they form on the surface of the organ. They collect into a common 

 trunk — the median spinal vein, which runs from before to behind, throughout 

 the whole extent of the superior groove in the spinal cord ; thus occupying an 

 analagous, though opposite, position to that of the artery of the same name. 

 From this vein escape, at intervals, emergent branches which open into the spinal 

 sinuses. 



Effluent Canals of the Dura Mater Sinuses. — "We have to notice, 

 under this designation, the veins which carry the blood from the sinuses, and 

 will consider in succession those which commence at the cranial sinuses, as 

 well as those that emerge from the interspinal canals. 



a. To be carried from the cranial sinuses, the blood flows into two kinds of 

 double gulfs, known as the parieto-temporal or subsphenoidal continents. 



The parieto-temporal confluents are lodged in the canals of the same name, 

 along with the mastoid artery. Each commences at the base of the internal 

 parietal protuberance, and terminates behind the supra-condyloid eminence. The 

 median and transverse sinuses are confounded with the superior extremity of 

 these reservoirs, and empty into them the blood coming from the encephalic 

 mass. This fluid is subsequently taken away by the superficial and deep temporal 

 veins, which have their principal radicles in these confluents. 



In Ruminants, the parieto-temporal confluent opens into the temporal veins, and has in 

 front a branch that passes to tlie fornmen lacerum basis crauii. In tlie Pig and Cat, it ia 

 lodged in the two grooves which open, one at the anterior foramen lacerum, the other at the 

 posterior. 



