Fig. 58.—Transverse Section through the Mesosoma of Limulus, to show the Anterior (A) and the Posterior (B) Surfaces of a Mesosomatic or Branchial Appendage. In each figure the branchial cartilaginous bar, "Br.C.", has been exposed by dissection on one side. "Ent.", entapophysis; "Ent.l.", entapophysial ligament cut across; "Br.C.", branchial cartilaginous bar, which springs from the entapophysis; "H.", heart; "P.", pericardium; "Al.", alimentary canal; "N.", nerve cord; "L.V.S.", longitudinal venous sinus; "Dv.", dorso-ventral somatic muscle; "Vp.", veno-pericardial muscle.