348 MISS E. J. BECK ON THE MUSCULAR 



They are united in a common attachment on the arthrodial membrane posterior to the 

 segment. 



There are no muscles attached to the chitinous investment of the postanal spine or 

 sting, though both 44 and 60 are attached to the arthrodial membrane connecting this 

 body with the sixth metasomatic segment. 



II. Dorso-Ventral Muscles. 

 The dorso-ventral muscles of the Scorpion lie near the longitudinal median line ; they 

 are attached dorsally and ventrally to sclerites. Certain other muscles may be classed 

 amongst the dorso-ventral muscles, which start from the tergites near the longitudinal 

 median line and run ventrally, but before reaching the ventral surface have been inter- 

 cepted by, and are attached to, the entochondrites. For the dorso-ventral muscles 

 see PI. LXXVII. figs. 1, 4, 5, and PL LXXVI1I. fig. 6. 



a. Prosoma. 



The dorso-chelicero-sternal muscle (61) is the most anterior of the dorso-ventral 

 muscles. It is very small, and is attached to the carapace near the median line ante- 

 rior to the central eyes ; it runs forward ventrally, and is attached to the arthrodial 

 membrane between the chelicerse. 



The median dorso-preoral entosclerite muscle (62) is a large muscle, between which 

 and its fellow of the opposite side are situated the eyes. It is attached dorsally to the 

 carapace, and ventrally to the preoral entosclerite (besides the figures above cited, see 

 PL LXXIX. fig. 12). 



The anterior dorso-plastron muscle (63) is attached dorsally to the carapace in the 

 median line, being joined to its fellow of the opposite side ; they separate and are 

 attached ventrally to the plastron. Through the arch thus formed pass the alimentary 

 canal and the dorsal vessel (see PL LXXX. fig. 13). 



The median dorso-plastron muscle (64) is attached dorsally to the posterior portion 

 of the carapace. It runs forward on the anterior surface of the posterior flap of the 

 plastron to the body of the plastron, to which it is attached (PL LXXX. fig. 13). 



b. Mesosoma. 



The posterior dorso-plastron muscle (65) is attached to the tergite of the first segment 

 of the mesosoma by the side of the pericardium. It runs forward, and at first lies 

 closely on the posterior surface of the posterior flap of the plastron ; it soon penetrates 

 the flap, and continues its course on the anterior surface until it reaches the body of 

 the plastron, to which it is attached. 



The dorso-suprapectinal-chondrite muscle (66) is attached to the second tergite of 

 the mesosoma by the side of the pericardium. It runs forward to the suprapectinal 

 chondrite, to which it is attached (see PL LXXIX. fig. 14). 



