AND ENDOSKELETAL SYSTEMS OF SCOEPIO. 349 



The dor so-ventral muscle (67) of the third segment of the mesosoma is attached to 

 the tergite of the third segment by the side of the pericardium. On passing to the 

 sternite of the third segment to which it is attached, it runs through the lateral antero- 

 posterior muscle (27) of the ventral longitudinal muscles, having a portion of the latter 

 muscle between itself and the lung-sac (see PL LXXVIII. figs. 8, 9). 



The dorso-ventral muscle (68) of the fourth segment of the mesosoma, the dorso- 

 ventral muscle (69) of the fifth segment of the mesosoma, and the dorso-ventral muscle 

 (70) of the sixth segment of the mesosoma are similar in position and character to the 

 dorso-ventral muscle (67) of the third segment of the mesosoma, being attached to the 

 tergites and sternites of the segments to which they belong. 



c. Metasoma. 

 The dorso-ventral muscle (71) of the first segment of the metasoma is similar to the 

 dorso-ventral muscles (67-70) of the mesosoma. There are no dorso-ventral muscles 

 in the following segments of the metasoma. 



III. Muscles attached to the Plastron or First Entochondrite. (Plate LXXVII. fig. 1, 

 and Plate LXXX. figs. 13, 14.) 



The plastron forms the base of attachment for many muscles, the larger number of 

 which are distributed to the appendages. In order to distinguish the muscles belonging 

 to the different appendages, I have called them " first," " second," &c, in reference to 

 the appendages to which they belong. Other muscles are distributed from the plastron 

 to the dorsal and ventral epidermal sclerites, to the epimeron, and to the suprapectinal 

 chondrite. 



The muscles between the plastron and the dorsal surface have been mentioned above 

 among the dorso-ventral muscles under the names of — 



The anterior dorso-plastron (63) ; 



The median dorso-plastron (64) ; and 



The posterior dorso-plastron (65) muscles. 



The anterior second coxo-plastron muscle (72) is attached posteriorly to the anterior 

 process of the plastron ; running forward, it is attached anteriorly to the second coxal 

 sclerite. 



The third deutomerite-plastron muscle (73) is attached to the anterior process of the 

 plastron. It runs into the third appendage, and is attached to the interior edge of the 

 deutomerite sclerite. 



The third postcoxal entosclerite-plastron muscle (74) is attached to the anterior 

 process of the plastron. It spreads out on the posterior surface of the third coxal 

 entosclerite, to which it is attached. 



The median second coxo-plastron muscle (75) is attached posteriorly to the body of 



