Musculoskeletal System

 As noted in the porpoise and in the sea lion anatomy areas, the musculoskeletal system consists of the muscles, bones, ligaments, and tendons, and teeth! In marine mammals, one of the first noticeable differences during a necropsy is the dark red color of the muscles compared with terrestrial animals. This color is especially distinctive in phocids, especially the deep divers such as elephant seals, because like all marine mammals, they store a significant portion of their oxygen supply for diving on myoglobin in the muscle.

During necropsy, the most common approach for pinnipeds is to place the animal in dorsal recumbence (on its back) and then make a cut the entire length of the ventral surface from chin to genital region. From there, you can use a knife or scalpel to dissect away blubber at the fascial surface and then the bulk of the muscle to the right and left of the central cut. In the neck region, cut carefully to expose the underlying trachea as well as parotid lymph nodes, salivary glands, and thyroid. Near the axilla, look for the prescapular lymph nodes just cranial to the scapula. When examining the muscle in any of these animals, note the color and texture. Pale color can indicate a young animal (myoglobin stores take several years to fully develop) or it could indicate trauma with excessive blood loss.

As you work your way through the carcass, it is useful to feel the bones in each region especially the jaw, ribs and vertebrae to check for injuries. Removal of the rib cage can be accomplished either by finding the articulation point (the joint) and cutting through each rib at this position or by using rib cutters (branch cutters from home depot work great). If using rib cutters it is especially important to thoroughly examine the ribs prior to making any cuts so you don’t miss or obscure any existing injury.

For more information about the musculoskeletal system of phocids see Rommel and Lowensteine (2001) and Pabst, Rommel, and McLellan, (1999).

 Detailed annotated images of the musculoskeletal system in two phocids, the harbor seal and elephant seal, are shown below.  CLICK on an image to see an enlarged view.