This runs down the anterior and outer side of the upper arm, and is attached to the proximal tendon of the extensor metacarpi radialis longus, a little below the outer condyle of the humerus.
Quadrate bone with single proximal knob.
The proximal portion forms the retractor muscles of themanubrium, or proboscis, well developed, for example, in Geryonia.
The longitudinal system is discontinuous, and is subdivided into proximal, medial and distal portions.
It appears to be primarily related to the organs of attachment and to have attained greater elaboration than the rest of the nervous system because the proximal end is the most specialized and most stimulated portion of the worm.