ARTHUR DEWITT WHEDON 405 



The Secondary Longitudinal Sternal Muscles (plate XXIII, 

 figure 8, sis). These thinner, band-Hke muscles are nearly par- 

 allel to the median line and are covered by the Primary set. In 

 segments two, three, and four a small anterior-lateral corner of 

 one of the muscles is not covered over. It is not clear how many 

 portions or divisions exist; in most segments there seem to be 

 two, but in other segments or in other specimens four divisions 

 appear to l)c present. They are always of uniform width through- 

 out. Wallengren shows two pairs of these to vnch segment, 

 slightly divergent posteriorly, in Aeschna grandis. 



The Tertiary Longitudinal Sternal Muscles (plate XXIII, 

 figure 8, tls). These are short, wide, and thin muscles l>ang 

 partly beneath the secondaries, and concealed by the overlying 

 muscles except at the inner mesal posterior corner. They have 

 their origin upon the face of the sternitc just posterior to the 

 level of the nerve ganglion and slightly interior to the margin of 

 the Primary Longitudinal Sternals. From these points they 

 converge caudad and insert upon the suture-fold. They are 

 here separated by a distance equal to the width of one of the 

 muscles. They are especially modified in the female. 



The Internal Tertiary Longitudinal Sternal Muscles (plate 

 XXIII, figure 8, itls). These are not represented in Aeshna 

 according to Wallengren or Matula. They are very slender, 

 cjdindrical muscles lying parallel and median to the last named; 

 they are stoutest in the anterior segments. As they originate a 

 very little farther forward than the Tertiary Longitudinal Mus- 

 cles they are the longer of the two. They insert ver}^ close to- 

 gether beneath the nerve cord. In the seventh segment of the 

 female they appear to associate with the oviducts and become 

 intersegmental; this is not perfectly clear, however. 



The Quaternary Longitudinal Sternal Muscles (plate XXIII, 

 figure 8, qls) are similar to the Tertiary Muscles but are smaller 

 and weaker, and located near the lateral edges of the sternum. 

 They are concealed by the Secondary Sternals. 



Segmental Muscles of the Tergum: — 



The Primary Longitudinal Tergal Muscles (plate XXIII, 

 figure 11, pit) correspond to the sternals of the same name and 

 lie in similar positions, but none of them arc di\aded as in the 



TRANS. AM. EXT. SOC, XLIV. 



