2,570. The Definition of "Severed"

Hilchos Shechita 9:1

“Severed” is as follows: if the skin that covers the marrow is severed, the animal’s a treifa. This is so as long as the greater part of its circumference is severed; if the skin is torn laterally or punctured, the animal remains permitted. Similarly, if the spine was broken but the spinal cord wasn’t split, or if the marrow is crushed so that it quivers, the animal remains permitted because the skin remains intact.

Hilchos Shechita 9:2

If the marrow deteriorates so that it can be poured like water or melted wax with the result that the spinal column can’t hold when it’s lifted, the animal’s a treifa. If it can’t hold because of its weight, then the situation is a case of doubt.