518 



PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



backward and inward. Thoy bond the frontal plab^s downward, and 

 thus assist in attachino- the biiudcs (a, li.u's. 1'4 and •2:>). 



'riierc ar«> (lircc pairs 

 of muscles which operate 

 in producinj^' flexion ])(>- 

 tween the cephalon and 

 the tliorax along the 

 cross-bar of the H -shaped 

 groo V e aire a d y de- 

 scribed. The shortest of 

 these three yiairs are the 

 nearest to tiie median 

 line and nearly paralhd 

 with it (b). The second 

 pair are very much larg- 

 er and extend from the 

 middle of the cross-har 

 frontward and outward, 

 at ail angle of -45 degrees, 

 to the very edge of the 

 carapace (c). 



The third pair are 

 again nearly parallel with 

 the mid line but much 

 farther away from it than 

 the tirst pair (d). 



The muscles for the 

 extension of the free 

 (fourth) thorax segment, 

 the genital segment, and 

 the abdomen arise side 

 b}" side in pairs near the 

 median line in the pos- 

 terior portion of the 

 thoracic area (e). The 

 outer pair are the short- 

 est and terminate near 

 the center of the fourth 

 segment, controlling the 

 movements of that seg- 

 ment. The pair next in- 

 side of these are the longest and extend through the genital segment 

 and into the al)domeii. 



The third or inner pair terminate in the genital segment. 

 In connection with these we find shorter muscles farther back aiis- 

 in<- near the center of the genital s(>gmeiit and terminating in the 



Flii. -Jl.— MrsrULATUIlE (IF A JIALE CAI.KirS fTRTUS. (AFTER 

 I'lCKEKlNG AM) Da.NA.) il, F1,EX()KS (IF FRONTAL PLATES; b, 

 C, (1, MFSCLES PK()I)l-CIN(i FLEXION BETWEEN THE CEPHALON 

 AND thorax; e, extensors OF FREE SEGMENT, GENITAL SE(;- 

 MENT AND ABDOMEN; f, EXTENSORS BETWEEN THE GENITAL 

 SEIiJIENT AND ABDOMEN; g, PRODUCE FLEXION BETWEEN THO- 

 RACIC AND LATERAL AREAS; ll. i, MOTOR MCSCLESOF THE SEC- 

 OND AND TIIIKll I.KOS: 1, MANimn.E MOTORS. 



