NORTH AMERICAN ODONATA. 175 



Second accessory of the posterior depressor (flexor radii quinti alaj secuuda' 

 Lend., additiouuel posterieur au abaisseur posterieur Pol.l lies on tbe inside of 

 the preceding and behind the posterior depressor ; it arises from tbe lower, an- 

 terior part of the metepimeron near tbe nietinfraepisternum, and inserts by a 

 cap-tendon into the wing-base below the post-costa, and immediately on the in- 

 side of the insertion of the first accessory, than which muscle it is somewhat 

 larger. 



Principal elevator of the hind wings (tensor alffi secundse Lend., elevateur Pol.) 

 takes its rise from the sides of the metathoracic neural canal and inserts by.a 

 very short, powerful cap-tendon into the extreme inner wing-base from costa to 

 median vein. Like tbe elevator of the front wings, it has a small muscle reach- 

 ing from its tendon of insertion to tbe fulcral process. 



Anterior accessory elevator (pronator alse secundse Lend., additionnel anterieur 

 au elevateur Pol.) arises from the outer upper margin of the third coxal opening, 

 and inserts by a cap-tendon into a process on the wing-base below the costa and 

 behind the level of the insertion of the anterior depressor. 



Posterior accessory elevator (supinator alse secundse Lend., additionnel poste- 

 rieur au elevateur Pol.) arises immediately behind the anterior accessory elevator 

 and inserts by a pale tendon into a process on the wing-base below the subcostal- 



Adductor radii quinti alse secundae Lend, arises on the metanotum opposite the 

 median vein and inserts on the post-costa. 



The relative positions of the muscles of the hind wings are the same as for 

 those of the front wings, and are shown in fig. 12, pi. II. 



Each wing, therefore, whether front or hind, has three elevators, 

 five depressors and one adductor. Certain of these acting by them- 

 selves produce different effects than mere elevation or depression. 

 Thus, the anterior depressor moves the wing horizontally forwards, 

 the adductor horizontally backwards; moreover, the surface of the 

 wings may be somewhat slanted from one plane to another. 



The position of the first lateral suture corresponds to the line of 

 separation between the muscles of the front and of the hind wing, 

 the arrangement of those of the latter repeating that of the former. 



Other thoracic muscles than those of the legs and wings are 



Auxiliary sterno-dorsal rising from the outer side of the hind end of the meta- 

 thoracic neural canal by tendon, and inserts by tendon into the tergum of the 

 first abdominal segment ; it lies close to the middle line and acts as an extensor 

 of the abdomen, in connection with the superior tergal abdominal muscles. 



Submedian ventral thoracico-abdominal arises with its fellow of tbe opposite side 

 from near the mid-ventral line of tbe metasternum, and inserts into the middle 

 of the interior margin of the first abdominal sternum. It is a flexor of the 

 abdomen in connection with the sternal abdominal muscles, with which it is 

 perhaps homologous. 



Lateral thoracico-ahdominal, with its fellow of the other side, arises by a com- 

 mon tendon from the roof of tbe metathoracic neural canal ; the bellies separate, 

 diverge, run backwards and insert by a pale tendon into the side of the anterior 

 margin of the first abdominal sternum; together they act as an abdominal 

 flexor, separately to pull the abdomen to that side. 



TEANS. AM. ENT. SOC. XX. JULY, 1893. 



