64 ON THE ANATOMY OF THE FLY. 



are inserted into the ento-thorax. Another process on each side is 

 formed by the turning in of the posterior superior angle of the sternum ; 

 it gives origin to a number of muscles connected with the wings, and 

 a broad muscular slip unites its inner edge with the external edge of the 

 superior surface of the ento-thorax. I propose the term para-pleuron 

 for this process. 



The meta-sternum is very narrow beneath, the posterior being 

 nearly approximated to the intermediate coxse. It forms, however, a 

 more considerable portion of the flank. Internally it bears a process in 

 the mesial line, the meta-thoracic ento-thorax, which supports the great 

 nerve trunk, the osscphagus, intestine, dorsal vessel, and salivary glands 

 in their passage to the abdomen. This process is very similar to the 

 ento-thorax of the meso-sternum, but is much narrower ; it almost meets 

 that process anteriorly. A pair of strong ridges extend from it laterally 

 along the anterior edges of the meta-sternum. It gives origin to several 

 pairs of muscles. 



The lateral plates of the pro-thorax are one on each side ( Plate V 

 Figs. 1, 5, and 8,) ; they are best seen internally, where their limits are 

 defined by ridges. They are almost square, but the superior anterior 

 angles unite them to the dorsal plate of this segment. Each is bounded 

 inferiorly by the coxa, posteriorly by the anterior thoracic spiracle, and 

 anteriorly by the condyle and anterior thoracic opening. 



The lateral plates of the meso-thorax are two on each side, the larger 

 is called the episternum, but the smaller, which is likewise posterior, does 

 not appear to have received a name. I shall call it the posterior lateral 

 plate of the meso-thorax, 



The episternum ( Plate V. Figs. 5 and 8 6) is almost square^and very 

 solid. Its superior posterior angle is prolonged into the thorax as a narrow 

 process, from which the anterior muscles of the wing arise. 



The posterior lateral plate ( Plate V, Fig, 5 ) is deeply notched above 

 for the insertion of the wing, but is otherwise nearly square ; a small 

 knob-like projection marks its anterior superior angle and is immedi- 

 ately in front of the insertion of the wing. 



The lateral plates of the meta-thorax are one on each side. They are 

 smaller than those of the meso-thorax, and are notched posteriorly for 

 the insertion of the halteres ; each is bounded below by the posterior 

 thoracic spiracle, anteriorly by the- posterior lateral plate of the meso- 

 thorax, above by the ra eta-thoracic tergum, and behind by the insertion 

 of the halter and the first abdominal segment. 



The tergum or dorsal plate of the pro-thorax (Plate V, Fig. 10 ) is 

 reduced to a narrow ridge, which thickens the edge of the anterior thoracic 

 opening and which gives off a pair of diverging processes posteriorly, for 

 the origin of muscles, These are connected near their base by a thin trian- 



