THE MUSCULAR SYSTEM. 259 



themselves contiguously to them at the mesothorax. They are most 

 distinct in the grasshoppers and Termites. In the Coleoptera several 

 are found upon each side, some of which come from the front and others 

 from behind from the back. I call them furcate dorsal muscles (mus- 

 culi furci-dw sales.) They are the Jlechisseur lateral de rapophyse 

 episternale posterieure, I'abaisseur du tergum, et I'abaisseur du dia- 

 phragme, of Straus. 



177- 



THE MUSCULAR SYSTEM OF INSECTS WITH A CONNATE THORAX. 



While in insects with a free prothorax the greatest portion of the 

 entire thorax is occupied by the metathorax, in those orders in which 

 the thoracic case is closely united together, the mesothorax preponderates 

 in a like manner. The Cicada make the transit to this conformation, 

 for in these insects, although they possess a free and moveable pro- 

 thorax, still the greatest space is occupied by the mesothorax. The 

 large muscles of attachment and muscles of connection consequently lie 

 in the mesothorax in insects of this structure and in the Hymenoptera, 

 and indeed between the prophragma and the mesophragma, or, when the 

 former is very small, between the mesonotum and the mesosternal plate. 

 In the first case, it is the dorsal muscles which are chiefly developed, 

 and, in the latter case, the lateral muscles of the back. We thus find it 

 in Cicada, whose enormous lateral muscles of the back nearly entirely 

 supplant the true muscles of the sides. In the Lepidoptera, on the 

 contrary, the true dorsal muscles are the largest, although the pro- 

 phragma is but small : they consequently originate from the anterior 

 portion of the mesonotum, and so increase that they occupy two-thirds 

 of the thoracic cavity. In the Diptera, lastly, the lateral muscles are 

 very large. They originate, as is always the case, from the lateral 

 ridges of the mesonotum, and pass on to the mesosternum in front of 

 the cavities of the coxae. In Eristalis tenax I have distinguished two 

 separated lateral muscles on each side, the most posterior of which 

 inserts itself between the cavities of the intermediate and posterior 

 coxae. But this is possible in the Diptera only, for in them the meso- 

 phragma is wanting, or, rather, is so small, that it may be considered as 

 deficient. The dorsal muscles, therefore, are also distended between 

 the mesonotum and the metaphragma, but do not run parallely with 

 the former, but incline more obliquely downwards. 



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