406 MORPHOLOGY OF THE ABDOMEN IN THE ODONATA 



case of the sternals of segments four, five, six, and seven. They 

 are much narrower at the anterior end. They are the most 

 ventral of the tergal muscles. 



The ' econdary Longitudinal Tergal Muscles (plate XXIII, 

 figure 11, sit) are very similar to the Primary Tergals, but lie 

 dorsal to them and slant in the opposite direction (converging a 

 trifle caudad). They seem frequently to be made up of four 

 divisions or bands, and are thinner than the primaries. 



The Tertiarj^ Longitudinal Tergal Muscles (plate XXIII, 

 figure 11, tit) are the analogs of the Tertiary Sternals. They are 

 dorsal to the Secondaries and converge caudad to their insertions 

 upon the suture-fold. Their origins are, as are those of the 

 remainder of the Tergal Muscles, upon the face of the tergite. 

 They are wide and short in the anterior and become longer and 

 more slender in the posterior segments. 



The Quarternary Longitudinal Tergal Muscles (plate XXIII, 

 figure 11, qlt) correspond to the Internal Tertiary Sternals. They 

 are dorsal to the Tertiary Tergals and in the first, second, and 

 eighth segments lie vertically over the medial portions of these, 

 but in segment seven they are entirely internal to the latter. 

 They are shorter than the tertiaries. 



The Quinar}^ Longitudinal Tergal Muscles (plate XXIII, 

 figure 11, qnlt) are very similar to the Quaternary but are scarcely 

 more than half as thick. They are . dorso-lateral in position, 

 and have their origins just dorsal to those of the Dorso-ventral 

 Segmental Muscles and above the lateral margin of the Primary 

 Secondary Tergals. 



The Sextic Longitudinal Tergal Muscles (plate XXIII, figure 

 11, sxlt) He above the Secondary Tergals somewhat nearer the 

 mid-dorsum than the Quinary Muscles. They are comparable 

 to the Quarternary Muscles in size, origin and insertion, but are 

 largest in the first segment and decrease to the ninth. In the 

 latter they each insert upon a sharp, horn-shaped, chitinous ] oint 

 which projects forward from the anterior end of the tenth segment. 

 These muscles are very clear in A7iax but are not shown by Wal- 

 lengren in Aeshjia. 



Thoracico- Abdominal Muscles : — 



The same sets of muscles occur here that were noted in Lestes, 

 their positions and attachments being very similar. They are 



