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., 6 /). It bounds the outer edge of 



FIG. 35. Dorsal view of the Thorax of the Blow-fly : /, Scutellum ; .2, scutum ; j>, 

 prescutum ; ./, scutal spine ; J, propterygium ; 6, costal, 7, subcostal and 

 hypocostal nervures forming the remigium ; S, patagium ; g, lobulus of the 

 wing; /o, .squamula ; //, squama; 12, scutellar bridge; /j, 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 (c, f, #, /^ the alar syndesmosis. Descend- 

 ing vertically from the dorso-pleural suture between the 

 plates numbered 18 and 28 is the mesopleural syndesmosis. 



