AND ENDOSKELETAL SYSTEMS OF SCORPIO. 347 
similar to the arthrodio-tergal obliquus muscle (45) of the first segment of the meta- 
soma. There are no corresponding muscles in the fifth and sixth segments of the 
metasoma. 
The superficial dorso-ventral muscle (49) of the first segment of the metasoma is 
attached to the arthrodial membrane posterior to the segment on the ventral surface, 
and bends round superficially to the tergite to which it is attached. This muscle is 
unlike any other, in that it starts on the ventral surface and bends round superficially 
to the tergite. 
Ventral.—The median antero-posterior muscle (50) of the first segment of the meta- 
soma is attached to the arthrodial membrane, anterior and posterior to the segment. 
It is similar to the median antero-posterior muscles in the mesosoma. 
The arthrodio-sternal rectus muscle (504) of the first segment of the metasoma is 
attached posteriorly to the arthrodial membrane posterior to the segment; running 
forward it is attached anteriorly to the sternite. 
The lateral antero-posterior muscle (51) of the first segment of the metasoma is 
attached to the arthrodial membrane anterior and posterior to the segment. ‘This 
muscle is similar to the lateral antero-posterior muscles (25-30) of the mesosoma ; but 
there is no further continuation of it in the following segments. 
The median antero-posterior muscle (52) of the second segment of the metasoma is a 
large muscle lying in the median line, and therefore not repeated on each side of the 
animal. It is attached to the arthrodial membrane anterior and posterior to the 
segment, 
The median antero-posterior muscle (53) of the third segment of the metasoma, the 
median antero-posterior muscle (54) of the fourth segment of the metasoma, and the 
median antero-posterior muscle (55) of the fifth segment of the metasoma are similar 
to the median antero-posterior muscle (52) of the second segment of the metasoma. 
There is no corresponding muscle in the sixth segment. 
The lateral arthrodio-sternal muscle (56) of the second segment of the metasoma is 
attached to the arthrodial membrane posterior to the segment; it runs forward and is 
attached to the sternite, and lies lateral to the median antero-posterior muscle (52). 
The lateral arthrodio-sternal muscle (57) of the third segment of the metasoma and the 
lateral arthrodio-sternal muscle (58) of the fourth segment of the metasoma are similar 
to the lateral arthrodio-sternal muscle (56) of the second segment of the metasoma. 
The lateral arthrodio-sternal muscle (59) of the fifth segment of the metasoma is a 
large muscle attached to the arthrodial membrane posterior to the segment. Some of 
the fibres run to the dorsal surface, and are attached to the tergal portion of the sclerite, 
whilst the others run forward and are attached to the sternal portion. 
The lateral arthrodio-sternal muscle (60) of the sixth segment of the metasoma is a 
large muscle, some of the fibres of which run dorsally and are attached to the tergal 
portion of the sclerite, whilst the others run ventrally and are attached to the sternite. 
