NO. 2 THORACIC MUSCLES OF THE COCKROACH — CARBONELL 7 



It must be understood that levators and depressors are discussed 

 from a morphological sense. The action of the muscles will lift or 

 depress the leg only when its position is perpendicular to the body. 

 Since the leg is almost parallel to the body, the levators will pull it 

 forward and slightly up, the depressors will push it back and slightly 

 down. This is the way that the hind legs usually work in the roach. 

 The middle legs form a slightly greater angle with the body than the 

 hind ones, and the front legs a still greater angle than the middle legs. 



All the levators of the leg have their origin within the coxa in each 

 of the legs. Of the three depressors, the two lateral, which are the less 

 powerful, originate also within the coxa, on the walls and rim. The 

 middle one (the one inserted on the proximal end of the trochanter, 

 just opposite the femur) has branches that originate within the coxa 

 and extracoxal branches. The extracoxal branches take their origin on 

 the tergum, pleural ridge, and pleural arm in the prothorax, and in 

 the same places plus sternal arm and basalar plate in the mesothorax 

 and metathorax. 



THE DORSAL AND WING MUSCLES 



It is in the musculature on the wings that the cockroach thorax dif- 

 fers widely from the normal scheme of wing-bearing segments as 

 given by Snodgrass (I, III). The dorsal longitudinal and oblique 

 muscles are present but they are small and "relatively unimportant 

 elements in the wing mechanism by comparison with those of most 

 insects" (I, p. 177). The vertical tergosternal muscles are missing en- 

 tirely, and no traces of them or substituting mechanism can be found. 



Cockroaches are not powerful fliers, but they do fly. Since it is 

 extremely difficult to analyze the mechanism of the flight by looking 

 at the alar muscles, only an enumeration is given of the muscles re- 

 lated directly or indirectly to the wings, which are essentially the same 

 in both segments of the pterothorax. 



Dorsal longitudinal and oblique muscles. — These are important 

 muscles in the flight of most insects ; in the cockroach they are weak 

 and probably not very important. The dorsal longitudinals are the 

 weaker, the obliques being stronger. Both are found also in the pro- 

 thorax, where the obliques are attached to a sclerite fastened to the 

 lateral part of the first phragma, very close to the base of the first 

 wing. 



Muscle of the basalar plate (pronator extensor of the wing). — In 

 both wing-bearing segments this muscle is one of the more important 

 branches of the powerful main depressor of the leg {135c in fig. 27, 

 ijyc in fig. 45). The size of this muscle seems to indicate that it plays 



