That's blood spotting and is restricted to muscles. I believe what George has shown us here are haemal nodes.
"Hemal nodes usually occur in the fat that lies along the vertebrae of the neck, near where the trachea is found. Hemal nodes may also occur in the abdominal cavity in the fat located along the vertebrae near the tenderloins. These nodes are numerous in ruminants (deer, elk, cattle, sheep), occur in small numbers in canids (dogs, coyotes, wolves), and are absent in many other animal species."
Taken from - DNR - Lymph Nodes Hemal Nodes
Going by the photograph thats what I took them to be.