54 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8>2 



It is impossible to determine, from an anatomical study alone, the 

 individual action of the muscles attached on the back of the head and 

 on the cervical sclerites (fig. 32 A, B), since their functions may vary 

 according to whether opposed sets of them act together or as antagon- 

 ists. It is evident that the dorsal muscles (fig. 32 A, 4/, 48, 49) and 

 the ventral muscles {55) may tilt the head up or down respectively by 

 pulling on opposite sides of the fulcrum of the cervical sclerites {g), 

 or also that they may turn the head laterally if both sets on either side 

 act as antagonists to those of the other side, while, finally, if they all 

 act together they would become retractors of the head. The dorsal 

 muscles of the cervical sclerites (A, B, 50, 57, 52, 55) must be the pro- 

 tractors of the head, since their combined pull would straighten the 

 angles between the two sclerites of each pair and thus push the head 

 forward. The oblique ventral muscles of the cervical sclerites (fig. 35, 

 5^) would appear to be accessory to the lateral movement of the 

 head. 



4/. First protcrgal muscle of the head (fig. 32 A). — A slender 

 muscle arising dorsally on protergum ; inserted dorso-laterally on post- 

 occipital ridge of head (PoR). 



48. Second protergal muscle of the head (fig. 2,- A). — A larger 

 muscle arising dorsally on third ridge {e) of protergum ; inserted with 

 41 on postoccipital ridge of head. 



4g. Longitudinal dorsal muscle of the neck and prothorax (fig. 



32 A). — A broad muscle from first thoracic phragma (iPh) to post- 

 occipital ridge of head just below 48. 



50, 57. Cephalic muscles of the cenncal sclerites (fig. 32 A, B). — 

 Origins on postoccipital ridge below 4§> ; both extend ventrally and 

 posteriorly, the first (^0) inserted on first cervical plate, the second 

 (57) on second cervical plate. 



5i>, 5J. Protergal muscles of the cervical sclerites (fig. 32 B). — 

 Origins dorso-laterally on protergum at lower end of first tergal ridge 

 (c) ; both extend ventrally and anteriorly, crossing internal to §0 and 

 57, to insertions on first cervical sclerite, the first muscle with a branch 

 {32a) to articular process (g) of head. 



34. Prostcrnal muscle of the first cervical sclerite (figs. 32 A, B, 



33 C, 35). — A horizontal, diagonal muscle arising on prosternal apo- 

 physis (figs. 2,2, 35) ; inserted anteriorly on first cervical sclerite of 

 opposite side (figs. 32 B, 35), the right and left muscles crossing each 

 other medially (fig. 35). 



55. First ventral longitudinal muscle (figs. 32 A, 33 A, 35). — A 

 broad, flat muscle from base of posterior arm of tentorium to apophy- 

 sis of prosternum (figs. 32 A, 35, SA). 



