48 THE SCOLYTID BEETLES. 



tebrate anatomy as is applicable to parts in insects having the same 

 or similar functions. Subsequently the writer's attention was called 

 to the fact that the same idea was suggested to Chabrier. 



In Dendroctonus the clavicle and coracoid processes are prominent 

 and clearly defined, the condyle of the former being definitely con- 

 nected with that of the head of the subcostal vein, which articulates 

 between the condyles of the clavicle process and scapular plate. 

 Chabrier's name clavicula has been adopted for the combined clavicle 

 and coracoid processes. 



Tergal processes (fig. 20). — The processes of the tergal area, which 

 have more or less important functions as articulatory accessories, 

 may be designated as prescutal, scutellar, and postscutellar. 



Prescutal process. — The prescutal process is represented by a tri- 

 angular extension of the posterior angle of the prescutum, and is of 

 primary importance as an accessory to the scapular plate. 



Scutellar process. — The scutellar process is represented by the thick- 

 ened lateral margin of the lateral impression and by the produced, 

 acute, anterior angle. It is attached along its lateral margin to a 

 pleural tendon connecting the pleural disk to the flexor and sub- 

 scapula. This process is also accessory to the flexor. 



Postscutellar process. — The postscutellar process is an extension or 

 arm of the anterior angle of the postscutellum, and has its apex 

 attached to the pleural disk and to the pleural hook. 



Lateral emargination. — What is termed the lateral emargination 

 is the emargination in the side of the scutum between the posterior 

 angle of the prescutum and the scutellar process. It is present in 

 most of the insects and appears to facilitate the functions of the flexor 

 muscle. 



Lateral impression. — The lateral impression is an impression to 

 accommodate the flexor plate when the wing is at rest. 



Basal elements. — The basal elements of the wing which function as 

 articulatory accessories are here referred to as head of costal vein, 

 scapular, subscapular, radial, medial, and flexor plates (fig. 30). 



Head of costal vein (i) . — The head of the costal vein is produced 

 beyond its fused connection with the head of the subcosta. It is 

 connected to the head of the clavicle by a ligament, and evidently 

 functions in extending the wing forward as well as in contributing to 

 other motions. 



Scapular plate (a) . — In form and fuinction the fundamental basal 

 plate, which we here call scapular plate, is very suggestive of the 

 scapula of vertebrates, but its peculiar functions require quite differ- 

 ent tergal connections. It is joined by ligaments to the prescutal 

 process and lateral margin of the prescutal lobe in such a manner as 

 to facilitate part of its functions — that of unfolding, elevating, and 

 depressing the wing. Its condyle articulates directly with the 



