Diagram of Spinal Column, Cord, and Nerve-exits (after Gowers).
FIG. 46.
Sarcoma compressing Cervical Cord, Case 17 of Table (E. Long Fox).
Before considering briefly the indications which point to the various levels of the cord as a possible seat of spinal tumor, it will be necessary also to make plain a few anatomical facts. It must be borne in mind, first, that the nerve-origins in the cord are never at the same level as their exits from the spinal canal, or, in other words, that the spinal segments do not correspond with the bodies of the same numerical vertebræ, and that there is, in fact, one more cervical segment than there are cervical vertebræ. The tendency is for the nerve-trunks to run downward before passing out of the canal, so that in every instance, without exception, from the medulla oblongata to the filum terminale the segments of the cord are above the corresponding vertebral body. This discrepancy increases as we descend the cord; whereas it is approximately correct to say of the cervical and dorsal regions that every segment is opposite the vertebral body which is numerically just above it, this difference becomes much greater in the lumbar and sacral regions. The cord itself terminates in the lumbar enlargement which ends opposite the interval between the first and second lumbar vertebræ. All the remainder of the canal is occupied by the descending trunks of the lumbar, sacral, and coccygeal nerves as they pass to their respective foramina, constituting the cauda equina. It must be recalled, however, that the vertebral bodies, lying very deep, cannot serve as guides, but that we are dependent upon the spinous processes as landmarks in diagnosis. These again differ in their levels from their respective vertebral bodies, as they are deflected at somewhat different angles at different regions of the spine. Gowers has illustrated these facts by a very graphic wood-cut9 (Fig. 45), from which the general rule may be drawn that each vertebral spine is about opposite the spinal segment which is numerically two places below it; thus the eighth dorsal spine is opposite the tenth dorsal segment, etc. The indications afforded by this exact anatomical knowledge have reference largely to the existence of pain on pressure and to any deformity of the bony structures. The cases as reported do not indicate that this method of research has been utilized, and it may possibly be of only theoretical importance; but it has been considered worthy of reference as an indication in diagnosis.
9 Diagnosis of Diseases of Spinal Cord, p. 6.