NO. 2 THORACIC MECHANISM OF A GRASSHOPPER — SNODGRASS 55 



5(5. Dorsal lateral neck muscle (fig. 32 A). — A band of slender 

 fibers from first phragma (iPh) inserted on base of neck mem- 

 brane (Cv). 



j/. Ventral lateral neck muscle (fig. 32 A, B). — A short, flat mus- 

 cle from anterior edge of prothoracic episternum (EpSi), inserted on 

 base of neck membrane (Cv). 



The prothorax is movable on the mesothorax by two oblique, lateral 

 intersegmental muscles on each side (fig. 32 A, ^8, ^p), and by three 

 pairs of ventral intersegmental muscles (figs. 32 A, 35, 60, 8y, 88). 



fj8. Tcrgo-pleiiral intersegmental muscle (fig. 32 A). — A broad 

 muscle of several sections, attached anteriorly on protergum behind 

 upper end of ridge d ; extends posteriorly and ventrally to interseg- 

 mental membrane just before upper end of mesepisternum {Epsz). 



5p. Stcrno-pleural intersegmental muscle (figs. 32 A, 33 A, 35). — 

 Attached anteriorly on upper end of prosternal apophysis (figs. 32 A, 

 33 A, SA) ; extends posteriorly and dorsally to dorsal end of anterior 

 margin of mesepisternum (EpSn). In some insects this muscle is at- 

 tached posteriorly on the anterior angle of the mesotergum. 



60. Second ventral longitudinal muscle (figs. 32 A, 33 A, 35). — 

 Extends between prosternal and mesosternal apophyses. Attached 

 anteriorly by broad base on prosternal apophysis ; tapers posteriorly to 

 attachment on anterior margin of mesosternal apophysis (fig. 35). 



The other two sternal muscles that move the prothorax are the third 

 and fourth ventral longitudinals (figs. 32 A, 35, 8/, 88) attached an- 

 teriorly on the first spina (iSpn), but they will be described with the 

 mesothoracic muscles. 



61. Sterna-spinal muscle (figs. 33 C, 35). — A very small muscle 

 arising on base of prosternal apophysis (SA) ; the two from opposite 

 sides converging posteriorly to insertions on anterior end of first spina 

 (iSpn). Since the spinasternum (Ss) is but little movable on the 

 prosternum (Si) in the grasshopper, this pair of muscles can act only 

 as tensors or levators of the spinasternum. 



The muscles that move the prothoracic leg of Dissosteira represent 

 the tergal promotor (fig. 11, /), the tergal remotor (/), and the 

 sternal remotor (L) of the primitive limb base, and the abductors (M) 

 and the adductors (N) of the coxa. A representative of the sternal 

 promotor (K) is absent in the prothorax of Dissosteira. The sternal 

 remotors function as posterior rotators of the coxa by reason of the 

 single articulation of the latter with the pleuron only ; in Dissosteira 

 one branch of the sternal remotor arises on the spina. 



