The spinal cord

In the fetus, the spine and the spinal cord are the same length but, since the spine grows more quickly than the spinal cord, the lower end of the cord gradually retreats upwards, reaching the level of L3 at birth and the lower border of L1 in the adult. For this reason, too, the anterior and posterior nerve roots become more and more oblique from above downwards so the lumbar and sacral nerve roots form a bundle, the cauda equina, which occupies the lower part of the spinal canal. The posterior root ganglia occupy the intervertebral foramina so that the roots do not unite until after this point. The spinal cord itself ends as the filum terminate, a thin fibrous band which is included in the cauda equina.

Fig.72.1

A map of the dermatomes.

The small diagram shows the regular arrangement of dermatomes in the embryo, before the limbs become fully developed

Fig.72.1

A map of the dermatomes.

The small diagram shows the regular arrangement of dermatomes in the embryo, before the limbs become fully developed

The spinal cord shows two enlargements in the cervical and lumbar regions, corresponding to the origins of the nerves that make up the limb plexuses. It is for this reason that the vertebral canal is larger in these regions, and they are also the regions of the greatest mobility. • The meninges: the meninges—the dura, pia and arachnoid—are continuous with those of the cranial cavity so that the subarachnoid space is also continuous and cerebrospinal fluid may be drained from the system or its pressure measured, by lumbar puncture. The subarachnoid space ends at the level of S2.

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