412 MORPHOLOGY OF THE ABDOMEN IN THE ODONATA 



Muscles Controlling the Anal Appendages and the Rectum: — 



These are present and differ in no essential respect from those 

 already described. 



Dorso-ventral, and Oblique Intersegmental Muscles: (Plate 

 XXIV, figures 13 and 15— 

 The Dorso-ventral Segmental Muscles are of two very distinct 

 types : 



(1) The Tergo-pleural Muscles (plate XXIV, figures 13, 15, 

 and 16) which are vertical, heavy, cylindrical muscles located in 

 the anterior half of each segment. They do not attach to the 

 sternum. Through the central segments they are made up of a 

 number (3 to 5) fascicles, but near the thorax they dwindle to one 

 fascicle each. The origin of each muscle is broad and is spread 

 over the tergite dorsal to the lateral margin of the Primary 

 Longitudinal Tergal Muscle, i.e., it is between the tergite and 

 the muscle named. As it runs directly ventrad it becomes 

 cylindrical. Its insertion covei's most of the anterior end of the 

 pleurite. 



(2) The Tergo-sternal IMuscles (plate XXIV, figure 15, dvts). 

 Each muscle has its origin upon a broad, roughly crescent-shaped 

 area of the tergum in the posterior part of each segment ventral 

 to the level of origin of the Tergo-pleural Muscle. Its insertion 

 is partly, or wholly, upon the lateral margin of the sternum near 

 its middle part. This muscle is thick, and as it passes from 

 tergum to sternum it twists about its axis as it bends around 

 the Tergo-pleural Muscle. If viewed in transverse section of the 

 body the two muscles are seen to cross like the bars of the letter X. 



The Dorso-ventral Obhque Segmental Muscles (plate XXIV, 

 figures 13, 15, and 16) arise in the same region of the tergum 

 as the tergo-pleurals but posterior to them. They slant caudad 

 and ventrad to the suture fold of the succeeding segment and 

 insert just in front of the Tergo-pleurals, and not far laterad 

 from the edge of the Primary Longitudinal Sternals. 



The Transverse Muscles : (Plate XXIV, figures 14 and 15) — 



The Subintestinal Transverse Muscle (plate XXIV, figures 14 

 and 15) is very distinct and relatively stronger than in Anax. 

 Its attachment is rather high above tergo-pleural suture of seg- 

 ment six near its anterior end. 



