680 LavuRA FLORENCE 
half is the wall of the pharynx capable of any dilatation, and there are 
inserted four muscles of which the two median are the largest. They 
originate in the dorsal wall of the head above the anterior lobes of the 
brain, and pass obliquely forward and downward to their point of insertion. 
Their contraction, while it may dilate the pharynx, would seem rather 
to draw it back to its resting position. 
Between the eye prominences and the neck three bands of muscle 
originate in the lateral: wall of the head. The median band extends 
farthest back and the ventral the next farthest, while the dorsal is the 
shortest. Just behind the antennae these bands unite in a common 
tendon which is inserted in the anterior lateral angles of the ‘‘ mandibles ”’ 
of Enderlein. In his first description of the mandibles (1904: 128-129) 
Enderlein did not see these tendons, but in his second paper (1905: 
629-630) he describes and figures them as the tendons of the mandibular 
flexors. He also figures tendons passing forward from the posterior 
lateral angle of the mandibles to the anterior wall of the head, and calls 
them the tendons of the mandibular extensor. Sikora (1916:16), however, 
describes these last as a uniformly thin strand passing from the ventral 
border of the triangular skeletal piece to the side of the underlip. In 
gross dissections the ‘‘ mandibles ”’ remain attached to the anterior wall of 
the head by this strand, but its true histological nature has not been deter- 
mined, since it has not been identified in any of the series of sections 
made through the head. Enderlein found the ‘‘ mandibles ”’ well developed 
only in the hog louse, but considered that the finding of the muscle tendons 
removed every doubt as to their morphological interpretation. Sikora 
(1916:13, 17), on the other hand, reserves the term ‘‘ mandible” for 
the already-mentioned structure lying between the upper and lower lips 
and adapted for biting or rasping. She calls the ‘‘ mandibles ”’ of Enderlein 
“ gewolbten Chitinplatten”’ or ‘ dreieckige Skelettstiicke,”’ and denies 
the possibility of their being mandibles on the ground of their position 
back in the head and their separation by the pharynx. She suggests two 
functions for them, namely, to draw the pharynx forward and to transmit 
to the true mandibles the motor impulse of the muscles. Since the ‘‘ man- 
dibles ”’ are attached to the lateral wall of the pumping pharynx and the 
buccal plate, the contraction of the tendon muse les would exert a backward 
pull on their anterior angle, and they, working as a lever, would serve 
to push forward the buccal plate and the pharynx, a function performed 
