680 Laura 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 phari,'nx and the 

 buccal plate, the contraction of the tendon nuisclcs would exert a l^ackward 

 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 



