Which instrument is appropriate for dissecting the external oblique muscle?

The appropriate choice for dissecting the external oblique muscle is curved Mayo scissors. These scissors are specifically designed for cutting and dissecting tissue with precision. Their shape allows for better visibility and access to deeper structures, which is particularly useful when working on layered abdominal tissues like the external oblique. The curved design facilitates a more controlled and efficient dissection without excessive trauma to surrounding tissues.

Scalpels are primarily used for making incisions and not for delicate dissection, making them less suitable for this specific task. Metzenbaum scissors, while also designed for dissection, are generally more appropriate for finer, softer tissues rather than the tougher fibers of the external oblique muscle. A needle holder is used for grasping needles during suturing, and while it serves an important role in surgical procedures, it does not have the function needed for dissecting muscle tissue. Thus, the curved Mayo scissors are the best instrument for this purpose due to their design and intended use in surgical dissection.