24 Annals Entomological Society of America [Vol. XIII, 



inserted into the roof of the pharynx at a short distance from 

 the median Une. The second (pr.d.2) originates in the front 

 above the clypeus and is inserted into the pharynx behind the 

 first. The third dilator (pr.d.3) is inserted into the roof of the 

 oesophagus just in front of the brain. Its origin is in the 

 epicranium in front and to one side of the median ocellus. A 

 fourth muscle is sometimes present. 



The Post-cerebral Dorsal Dilator (Fig. 6, pst.d.) originates 

 in the epicranium immediately in front of the adductor of the 

 mandible and is inserted into the oesophagus just behind the 

 brain and a short distance from the dorsal median line. 



The Lateral Dilator (Fig. 5, l,d.) arises in the epicranium 

 at the inner side of the compound eye and is inserted into the 

 lateral median line of the oesophagus beneath the brain. 



The Ventral Dilators (Fig. 6, v.d.) are two rows of small 

 muscles which originate from the upper surface of the central 

 plate of the tentorium and are inserted into the lower wall of 

 the oesophagus a short distance on each side of the median 

 line. 



(d). Cervical Muscles. 



(Figs. 18 and 19.) 



The muscles which control the movements of the head may 

 be classified as depressors, elevators, retractors and rotators 

 ■of the head. 



LONGITUDINAL MUSCLES. 



(a) Sternal. 



1. The Inner Depressors of the Head originate from the 

 •enlarged basal portions of the pro-entosternites and are inserted 

 into the middle of the hind edge of the central tentorial plate. 

 1137, 5th sternal muscle of the veracervix]. 



2. The Outer Depressors of the Head originate immediately 

 laterad of the preceding, and are inserted into the dorsal surface 

 of the central tentorial plate. [136, 4th sternal muscle of the 

 veracervix]. 



3. The Short Depressor of the Head, origin, pro-entosternite, 

 insertion, into the cervical membrane just beneath the ventral 

 angle of the interpleurite. [135, 3rd sternal muscle of the 

 veracervix]. 



