AND ENDOSKELETAL SYSTEMS OF SCOEPIO. 345 



posterior end to the lateral portion of the arthrodial membrane at the posterior angle 

 of the segment. It bends round to the tergite, to which it is attached. 



The latero-dorsal muscle (16) of the second segment of the mesosoma ; the latero- 

 dorsal muscle (17) of the third segment of the mesosoma; the latero-dorsal muscle (18) 

 of the fourth segment of the mesosoma ; the latero-dorsal muscle (19) of the fifth segment 

 of the mesosoma ; and the latero-dorsal muscle (20) of the sixth segment of the meso- 

 soma, are all similar in form and position to the latero-dorsal muscle (15) of the first 

 segment of the mesosoma. 



Ventral. — The median anteroposterior muscle (21) of the third segment of the 

 mesosoma runs along the median line from the arthrodial membrane anterior to the 

 sternite, to the arthrodial membrane posterior to the sternite. As this muscle is in the 

 median line it is not repeated on each side of the animal (PI. LXXVII. fig. 3). 



The median anteroposterior muscle (22) of the fourth segment of the mesosoma ; the 

 median antero-posterior muscle (23) of the fifth segment of the mesosoma; and the 

 median anteroposterior muscle (24) of the sixth segment of the mesosoma, are similar 

 to the median antero-posterior muscle (21) of the third segment of the mesosoma. 



The lateral antero-posterior muscle (25) of the first segment of the mesosoma is 

 attached anteriorly to the plastron, and posteriorly to the suprapectinal chondrite 

 (PI. LXXX. fig. 14). 



The lateral antero-posterior muscle (26) of the second segment of the mesosoma is 

 attached anteriorly to the suprapectinal chondrite, and posteriorly to the sternite of 

 the third segment (PL LXXVII. fig. 3, and PI. LXXIX. fig. 14). 



The lateral antero-posterior muscle (27) of the third segment of the mesosoma is a 

 similar muscle to (26), but is attached anteriorly to the sternite of its own segment, 

 and posteriorly to the sternite of the following segment. This muscle is lateral to the 

 median antero-posterior muscle (21) of the first segment of the mesosoma. 



The lateral antero-posterior muscle (28) of the fourth segment of the mesosoma, and 

 the lateral antero-posterior muscle (29) of the fifth segment of the mesosoma are 

 similar to the lateral antero-posterior muscle (27) of the third segment of the meso- 

 soma, and are attached anteriorly to the sternite of the segment to which they belong 

 and posteriorly to the sternite of the following segment. 



The lateral antero-posterior muscle (30) of the sixth segment of the mesosoma is 

 similar to the lateral antero-posterior muscle (27) of the third segment of the meso- 

 soma, except that it is attached anteriorly to the sternite of the sixth segment, and 

 posteriorly to the arthrodial membrane posterior to the segment. 



The arthrodio-sternal obliquus muscle (31) of the third segment of the mesosoma is 

 a small muscle superficial to the lateral antero-posterior muscle (27), attached poste- 

 riorly to the arthrodial membrane posterior to the segment. It runs obliquely forward 

 towards the median line, and is attached anteriorly to the sternite. 



The arthrodio-sternal obliquus muscle (32) of the fourth segment of the mesosoma, 



3p2 



