NO. 3 



INSECT HEAD SNODGRASS 



151 



The muscles of the prothorax of the American tent caterpillar, 

 Malacosoma americana, are illustrated in figure 57. At A are shown 

 the lateral and ventral muscles as seen from a posterior dorsal view, 

 with the head turned somewhat downward on the neck ; B shows the 

 dorsal muscles as seen from below; C presents an inner view of all 



Fig. 57. — Muscles of the prothorax of a caterpillar, Malacosoma americana. 



A, prothoracic muscles inserted on lateral and ventral parts of back of head, 

 and ventral muscles of mesothorax, posterior view. B, dorsal muscles of pro- 

 thorax and mesothorax inserted on dorsal half of back of head, seen from 

 below. C, innermost layers of muscles of right half of prothorax, internal 

 view. D, external muscles of right half of prothorax. 



Isg, intersegmental fold ; Li, base of prothoracic leg ; PoR, postoccipital 

 ridge of head ; s, edge of tergal plate of prothorax ; iSp, first spiracle ; Tnt, 

 transverse bar of tentorium ; vap, ventral apodemal plate of postoccipital 

 ridge. 



the muscles in the right half of the prothorax inserted on the head ; 

 and D gives the muscles of the same side that lie external to those 

 shown in C, except the single fiber arising just dorsal to the spiracle, 

 which is shown in both figures. 



