English: View from below of a scorpion (Buthus occitanus) opened and dissected so as to show the pericardium with its muscles, the lateral arteries, and the tergo-sternal muscles.

PRO, Prosoma.
dpm, Dorso-plastral muscle.
art, Lateral artery.
tsm¹, Tergo-sternal muscle of the second (pectiniferous) mesosomatic somite; this is the most anterior pair of the series of six, none are present in the genital somite.
tsm⁴, Tergo-sternal muscle of the fifth mesosomatic somite.
tsm⁶, Tergo-sternal muscle of the enlarged first metasomatic somite.
Per, Pericardium.
VPM¹ to VPM⁷, The series of seven pairs of veno-pericardiac muscles.

There is some reason to admit the existence of another more anterior pair of these muscles in Scorpio; this would make the number exactly correspond with the number in Limulus polyphemus.
(After Ray Lankester, Trans. Zool. Soc. vol. xi, 1883.)