English: View of the ventral surface of the mid-line of the prosomatic region of Limulus polyphemus. The coxae of the five pairs of limbs following the chelicerae were arranged in a series on each side between the mouth, M, and the metasternites, mets.

sf, The sub-frontal median sclerite.
Ch, The chelicerae.
cam, The camerostome or upper lip.
M, The mouth.
pmst, The promesosternal sclerite of chitinous plate, unpaired.

mets, The right and left metasternites (corresponding to the similarly placed pentagonal sternite of Scorpio). Natural size.
(After Ray Lankester.)