Transverse section of A. nigrofasciata at 6 days post fertilization.Note the grey scale for the upper pharyngeal jaws and skull has a large range. Muscles overlap this range, preventing the use of voxel intensity to determine tissue. All structures of interest come into contact with similar intensity voxels, which causes the selection by automatic tools such as the "magic wand" to leak into adjacent areas and make them unreliable. Instead, two muscle groups (levator externus 4 and levator internus lateralis) are segmented manually here as shown by their red outlines, and this process is repeated for each structure through all images from each scan.