THE THORACIC EXO-SKELETON. 



167 



The Scutellum (/) is a pouch-like projection overhanging the 

 posterior part of the thorax and the base of the abdomen 

 (Plates VII. and VIII.)- It is connected with the scutum by a 

 pair of divergent ridges, which arise from its outer anterior 

 angles; these are the scutellar bridges of Loew [77]. De- 

 scending from the root of the scutellar bridge, a process of 

 the scutellum forms the upper edge of the posterior alar- 

 apophysis (Plate VII., b /). It bounds the outer edge of 



Fig. 35.— Dorsal view of llic Thorax of the Hlow-fly : /, Scutellum ; 2, scutum ; 3, 

 prcscutum ; 4, scutal sjiine ; J, proplerygium ; 6, costal, 7, subcostal and 

 hypocostal nervures forming the remigiuni ; S, patagium ; 9, lobulus of the 

 wing ; 10, scjuamula ; //, squama ; 13, scutellar bridge ; 13, posterior alar 

 apophysis. 



the supra-tympanic fissure, and the great wing scale (//) is 

 attached to it. 



The Lateral Aspect is represented in Plate VII., Fig. i. 

 Near its anterior margin the large anterior spiracle (/p) will 

 be readily recognised by its orange-yellow colour. Start- 

 ing from the upper margin of the spiracle, and extending 

 back to the wing root h, there is a deep suture, the dorso- 

 pleural suture. It is the anterior part of an extensive 

 syndesmosis {e, f, g, h), the alar syndesmosis. Descend- 

 ing vertically from the dorso-pleural suture between the 

 plates numbered i8 and 28 is the mesopleural syndesmosis. 



