AND ENDOSKELETAL SYSTEMS OF SCORPIO. 355 



of the carapace. It runs inwards, and is attached to the posterior part of the first coxal 

 entosclerite. 



The posterior first dorso-coxal entosclerite muscle (121) is attached posteriorly to the 

 carapace. Running forwards, it is attached to the exterior edge of the first coxal 

 entosclerite. 



The third dorso-coxal entosclerite muscle (122) is a thin broad muscle attached to 

 the carapace towards its lateral portion and to the posterior margin of the posterior 

 third coxal entosclerite. 



The fourth dorso-coxal entosclerite muscle (123) is attached to the carapace and to 

 the posterior margin of the posterior fourth coxal entosclerite. 



Mesosoma. — To the first appendage of the mesosoma, or genital operculum, there is 

 only one muscle, which is attached to the plastron, and has been already mentioned 

 with the muscles which are attached to the plastron as the seventh plastron muscle 

 (85). (See PL LXXX. figs. 13, 14.) 



To the second appendage, or pectine, there are six muscles, four of which are 

 attached to the suprapectinal chondrite, and have been already mentioned with the 

 muscles attached to the suprapectinal chondrite as the posterior (88), anterior (90), 

 interior (91), and exterior (92) pectino-suprapectinal-chondrite muscles (see PL LXXIX. 

 fig. 14). 



The epimero-pectinal muscle (124) is attached to the epimeron by the postero-lateral 

 portion of the interior margin of the sixth coxal sclerite. It runs into the pectine 

 (fig. 8). 



The sterno-pectinal muscle (125) is attached to the sternal sclerite, on which the 

 pectines are carried near the median line ; it runs laterally, and is attached to the 

 interior portion of the opening of the pectine (PL LXXIX. fig. 14). 



No muscles are attached directly to the lung-books, although there are two series 

 of muscles by which they are influenced. Amongst the ventral longitudinal muscles 

 will be seen the post-stigmatic muscles (35, 36, 37, & 38) of the third, fourth, fifth, 

 and sixth segments of the mesosoma; these are attached to the posterior edge of the 

 stigmata and to the arthrodial membrane posterior to the segment in which they 

 occur. 



The muscles of the other series run ventralwards from the pericardium, and spread 

 out on the surface of the blood-holding lung-sac in those segments in which the lung- 

 books occur. Of this series I shall speak later under the heading of " Muscles to the 

 Pericardium." 



VII. Muscles to the Epimeron. (Plate LXXVII. fig. 1, and Plate LXXVIII. fig. 6 ) 

 Muscles are distributed to the epimeron from the carapace, the plastron, the second 

 entochondrite, and the pectines. All of these have been mentioned above, with the 

 exception of those from the carapace. 



