264 ANATOMY. 



bent and gradually widening process, which is provided on each side 

 with a longitudinal groove (the same, &.), to which a corresponding 

 process of the inner margin of the metaphragma fits. Besides the 

 abdomen and thorax are still more intimately bound by means of a 

 flexible membrane surrounding the large aperture (the same, fig. 7 an( l 

 8. A, A.). I have also plainly distinguished two flat lateral muscles, 

 which pass from one part to the other. 



The connecting muscles of the abdominal plates may be divided into 

 the dorsal and ventral muscles. 



The dorsal muscles are two large, broad, but flat band-shaped 

 muscles, which run from the first to the last abdominal segment, and 

 are throughout intimately united with the connecting membrane of 

 every pair of plates. 



The ventral muscles are smaller, and do not pass in one line., but 

 only between every two contiguous ventral plates, taking an inward 

 oblique direction, so that their exterior boundary forms a zig-zag line. 



I also found in Locusta transverse ventral muscles, which originating 

 from the descending ends of the dorsal plates, run transversely 

 across the ventral plates. They contract the cavity of the abdomen, 

 and thereby especially promote expiration. The abdominal muscles in 

 general seem less to connect the segments than to promote the freer 

 expiration of the air. 



The remaining muscles of the abdomen, which raise and sink the 

 last plate, and at the same time unite the cloaca with the surrounding 

 parts, are subjected, like that organ itself, to so many differences, that 

 a general description will be possible only when a tolerable number of 

 insects of all orders and families shall have been examined. From all 

 observations hitherto made it appears that both the dorsal and ventral 

 plates receive an extensor and a flexor, which originates from the penul- 

 timate plate, and affixes itself to the terminal one, the former more 

 exteriorly and anteriorly, and the latter more interiorly between the 

 preceding, and extending further to the apex. 



The muscles of the cloaca and of the colon originate from the cir- 

 cumference of those organs, and pass as broad and flat bands to the 

 dorsal and ventral plates, surrounding them. Both only serve to 

 retain the cloaca* and colon in their places when the faeces are 

 voided from the latter, or when the vagina or penis are protruded from 

 the former. 



The muscles peculiar to the penis and the vagina,_ lastly, differ as 



