A. R. TAYLOR (Dundee) noted that there were four theories regarding the method of formation of syringomyelic cavities. They were:1. That they were primary congenital dilatations of the central canal, or that they were secondary to obstruction of a spinal blood vessel.2. That they resulted from diversion of ventricular CSF down the central canal of the cord in the presence of obstruction to the exit foramina of the fourth ventricle.3. That CSF was driven down the central canal of the cord if jugular venous pressure were increased in the presence of blocks to the exits from the foramen magnum and fourth ventricle as a result of impaction of the cerebellar tonsils.4. That areas in the postcentral areas of the cord became filled by CSF after necrosis in these situations. The spaces filled with fluid became enlarged in an upwards direction under the influence of increased spinal pressure caused by coughing or any other manoeuvre simulating the Valsalva phenomenon.In the investigation described, plastic tumours had been implanted in the subarachnoid space of monkeys and rats at different levels to cause venous congestion and small haemorrhages in the grey matter only at distances cranial or caudal to the obstructions. It was concluded that the venous drainage of the grey matter runs downwards below the first dorsal spinal segment and upwards above this level. There were three longitudinal segments in the pattern of venous drainage, the first being from the foramen magnum to the first dorsal segment level, the second being from the first dorsal to the eighth dorsal segment level, and the third being from the eighth dorsal to the fifth sacral segment. Placement
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