(c) Spinal Cord.—Islands of gray substance are sometimes found within the white medullary tissue, particularly- in the posterior columns of the lumbar portion of the cord (also in the medulla oblongata). These anomalies of distribution, however, have no clinical interest and in that respect may be compared to the lateral furrows around the cervical enlargement and around the cord, which are particularly well seen in defects of the py-ramidal tract.
There are several varieties of congenital changes of the central canal, which may possibly assume clinical significance. Aside from a moderate local dilatation of the central canal, pear-shaped in cross section with a long dorsal process ("simple hydromyelia," Zappert), the central canal in newborn infants or somewhat later in life is occa sionally greatly dilated, forming a number of diverticula or even com pletely open at the dorsal wall. This congenital form, in addition to its genetic interest, is significant because it may possibly bear some relation to a subsequent syringomyelia, a theory which finds support in the fact that proliferation of the neurogliar tissue is sotnetimes ob served in the (dilated central canal in young infants (and possibly also in the newborn?). The majority of those who have investigated the question of syringomy-elia nowadays incline to the VieW that the condi tion begins in a congenital defect, which possibly finds expression in congenital hydromyelia and early proliferation of the neurogliar tissue (see Schlesinger's monograph).
These anatomical anomalies occuring during infancy do not give rise to clinical symptoms. If we admit the possibility that many forms of syringomyelia develop frotn these early changes, it is not surprising that syringOnlyelia in infancy is practically without clinical symptoms; for it takes some time before the abnormal formations in the spinal marrow attain sufficient extent to produce clinical disturbances. Indefi nite prodromal symptoms, not ascertained until later in taking the history of a case of sytingomyelia in a youthful subject, may possibly occur during childhood. Except for these, however, syringomyelia is not a children's disease and its discussion in this work seems superfluous.
Occasionally a condition known as diastentatonigelia, in which the spinal cord is dhided into two portions, particularly in the lower dorsal and lumbar regions, is observed at the autopsy table. The develop ment of the two halves of the spinal cord may be approximately equal, or one half may greatly exceed the other in size and development. The rudimentary development of two spinal cords has also been ob served. The condition is interesting from a pathological view point only. As a rule it is associated with other malformations of the central nervous system, especially spina bifida.