8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. lO/ 



an important role in the flight. Snodgrass (III, pp. 235 and 240) 

 points out its role as pronator and extensor of the wing. 



Muscle of the suhalar plate (depressor-extensor of the wing. 128 

 in fig. 27, i6g in fig. 42). — Powerful muscle which originates on the 

 meron. As in the preceding one, its size seems to indicate its im- 

 portance in the flight besides its action as extensor, which has been 

 pointed out by Snodgrass (III, p. 240). The same author (III, p. 

 234) shows its importance in the downstroke of the wings. 



Pleuro-alar muscle (flexor of the wing. 115 in fig. 25, 158 in fig. 

 44) . — Small muscle from the pleural ridge to the third axillary {3 Ax, 

 figs. 21 and 36). Its action in the wing flexion has been described 

 by Snodgrass (III, pp. 237 to 240). 



Muscles of the anterior notal wing process. — In both wing-bearing 

 segments, a flat muscle that originates on the anterior edge of the 

 pleural arm and pleural ridge {116 in fig. 25, 159 in fig. 40), and in- 

 serts on the downward-bent portion of the anterior notal wing process, 

 which articulates with the first axillary {lAx in figs. 21 and 36). It 

 is the first of a series of three muscles which ends on the posterior 

 portion of the coxal rim, the second being between the pleural and 

 sternal arms, the third between the latter and the coxa. Its probable 

 action on the wing movements is difficult to explain. 



II. LIST OF THE THORACIC MUSCLES 



The numeral 52 has been given to the first thoracic muscle consid- 

 ering that 51 muscles have been found in the head. Each number in the 

 list represents one pair of muscles located symmetrically on each side 

 of the body. 



NECK AND PROTHORAX 



52. First cervical muscle of the head (fig. 17). — A flat, fan-shaped 

 muscle, arising from the dorsal cervical sclerite, inserted laterally 

 on postoccipital ridge of the head. 



5J. Protergal muscle of the head (fig. 17). — A large, flat muscle, 

 arising from the medial line of protergum, inserted laterally on 

 the postoccipital ridge, just below the insertion of ^2. 



54. Second cervical muscle of the head (fig. 17). — Slender, flat mus- 

 cle, arising dorsally from the cervical integument, tapering to its 

 insertion on the tentorial bridge of the head. 



55. Longitudinal ventral muscle of the head and prothorax (figs. 6, 

 17). — A medium-size, ribbon-shaped muscle, from base of the 

 sternal arm to median part of tentorial bridge of the head. 



