AND ENDOSKELETAL SYSTEMS OF SCORPIO. 549 
The dorso-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. LX XVIII. 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. 
ce. 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. 
II. Muscles attached to the Plastron or First Entochondrite. (Plate LXXVIL. 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 
