“842 THE VASCULAR SYSTEM. 
borders. Each sinus communicates with the middle meningeal veins, receives veins 
from the dura mater, and terminates in the anterior part of the corresponding 
cavernous sinus. 
Superior Petrosal Sinuses.— Each fa cas petrosal sinus (s. petrosus 
superior) commences at the apex of the petrous portion of the temporal bone in 
the posterior end of the corresponding cavernous sinus. It runs backwards and 
outwards in the attached margin of the tentorium cerebelli, above the fifth cranial 
nerve, and grooves the upper border of the petrous portion of the temporal bone, 
at the outer extremity of which it terminates in the lateral sinus at the point where 
the latter is turning downwards on the inner surface of the mastoid portion of the 
temporal bone. It receives inferior cerebral, superior cerebellar, tympanic, and 
diploic veins. 
Inferior Petrosal Sinuses.—An inferior petrosal sinus (s. petrosus inferior) 
commences at the posterior end of each cavernous sinus; it runs backwards, out- 
wards, and downwards in the posterior fossa of the cranium, in a groove along the 
lower margin of the petrous portion of the temporal bone and the adjacent border 
of the basilar portion of the occipital bone, to the anterior compartment of the 
jugular foramen of the same side, through which it passes. It crosses the last four 
cranial nerves either externally or internally, and it terminates in the internal 
jugular vein. Its tributaries include inferior cerebellar veins and veins from the 
internal ear, which pass to it through the internal auditory meatus, the aqueductus 
cochlea, and the aqueductus vestibuli, 
THE SPINAL VEINS. 
The spinal veins include— 
(1) The extra-spinal veins. 
(a) The anterior spinal plexus. 
(ob) ,, posterior - 
(2) The veins of the bodies of the vertebree. 
(3) The intra-spinal veins. 
(a) The anterior longitudinal veins. 
(6) ,, posterior - 53 
(4) The veins of the spinal cord. 
The anterior spinal plexus lies in front of the bodies of the vertebrae. It consists 
of a number of relatively small anastomosing channels, which communicate with the 
veins of the bodies of the vertebrze, and which receive tributaries from the adjacent 
muscles and ligaments. Its efferent vessels terminate in the cervical region in the anterior 
deep cervical vein, in the dorsal region in intercostal veins, in the lumbar region in the 
lumbar veins, and in the sacral region in the lateral sacral veins. 
The posterior spinal plexus consists of numerous anastomosing venous channels 
which lie on the laminze and round the spines and the articular and transverse processes 
of the vertebre. The plexus receives tributaries from the muscles and skin of the 
back, and communicates, through the ligamenta subflava, with the posterior longitudinal 
spinal veins in the interior of the spinal canal. Its efferent vessels pass between the 
transverse processes of the vertebree, or through the sacral foramina, and terminate in 
the vertebral, the intercostal, the lumbar, and the lateral sacral veins respectively. 
Veins of the Bodies of the Vertebre.—The cancellous tissue of the bodies of the 
vertebrae is permeated by large venous channels which communicate anteriorly with the 
anterior spinal plexus. These channels terminate posteriorly in the vene basis vertebre, 
which open into transverse anastomosing vessels which connect the anterior longitudinal 
spinal veins. 
Anterior Longitudinal Spinal Veins. —Two anterior longitudinal spinal veins collect 
blood from the bodies of the vertebrae, from the adjacent ligaments, and from the spinal 
dura mater. They are plexiform vessels which extend from the foramen magnum, behind 
the bodies of the vertebrae and along the margins of the posterior common ligament, to 
the coccyx, and they are connected together, opposite each vertebral body, by ‘transverse 
anastomoses which lie between the posterior common ligament and the bodies of the 
vertebree ; these transverse anastomoses are greatly dilated opposite the centres of the 
bodies where they receive the ven basis vertebre. Each anterior longitudinal spinal 
vein communicates round the margin of the canal with the corresponding posterior vein, 
