Spinal cord

 Spinal cord

Medulla spinalis

The spinal cord, one of the two major structures of the central nervous system, is an elongated, nearly cylindrical structure that occupies the upper two-thirds of the vertebral canal. Its average length in the male is about 45 cm and in the female is about 42 to 43 cm; its weight amounts to about 30 grams. 

The spinal cord extends from the upper border of the atlas to the lower border of the first,

or upper border of the second, lumbar vertebra. Above, it is continuous with the brain; below, it ends in a conical extremity, the conus medullaris.

 A fibrous filament called the filum terminale extends from the apex of the conus medullaris to the back of the first segment of the coccyx.

The spinal cord does not completely fill the spinal canal and, like the brain, is surrounded by three membranes,

from outer to inner: the dura mater, the arachnoid mater, and the pia mater.