What is "spinal marrow"

Marrow \Mar"row\, n. [OE. marou, mary, maruh, AS. mearg, mearh; akin to OS. marg, D. merg, G. Mark, OHG. marg, marag, Icel. mergr, Sw. merg, Dan. marv, Skr. majjan; cf. Skr. majj to sink, L. mergere. [root]274 Cf. Merge.]

1. (Anat.) The tissue which fills the cavities of most bones; the medulla. In the larger cavities it is commonly very fatty, but in the smaller cavities it is much less fatty, and red or reddish in color.

2. The essence; the best part.

   It takes from our achievements . . . The pith and marrow of our attribute.
   --Shak.

3. [OE. maru, maro; -- perh. a different word; cf. Gael. maraon together.] One of a pair; a match; a companion; an intimate associate. [Scot.]

   Chopping and changing I can not commend, With thief or his marrow, for fear of ill end.
   --Tusser.

   Marrow squash (Bot.), a name given to several varieties of squash, esp. to the Boston marrow, an ovoid fruit, pointed at both ends, and with reddish yellow flesh, and to the vegetable marrow, a variety of an ovoid form, and having a soft texture and fine grain resembling marrow.

   Spinal marrow. (Anat.) See Spinal cord, under Spinal.