22 bulletin: museum of comparative zoology. 



rod (hac^ is situated in a lateral concavity of the ligula (Plate 4, Figs. 

 29, 30, gls.), and consequently underlies the lateral margin of the para- 

 glossa. The significance of the chitinized rod, or tendon, and its liga- 

 ment, I shall presently show when describing how the head of the 

 maxilla is abducted. 



There are ten separate muscles which belong to each maxilla, exclud- 

 ing those of the palpi ; like the muscles of the mandibles, they are most 

 conveniently studied in frontal sections, although these must be supple- 

 mented by sections in other planes, as well as by dissections. The max- 

 illae are more complicated than the mandibles, and are correspondingly 

 more difficult to understand ; after long study, however, I have but 

 little doubt as to their structure and movements. 



1. Retractor and abductor. A long, slender muscle (Fig. 20, 1. ret. 

 abd.), which arises immediately beneath the origin of mandibular mus- 

 cle No. 7 (Fig. 14) on the same median dorsal projection, and passes 

 forward, outward, and downward to be inserted on the anterior con- 

 cavity of the cardo (cf. Fig. 18). This muscle appears to retract and 

 slightly abduct the entire maxilla by pulling the cardo backward. The 

 retraction must be of slight amount, however, as the two ligaments 

 which attach the cardo to the foot of the glossa prevent any extensive 

 retraction or protrusion. 



2 and 3. Adductors, Two cylindrical muscles, distinct from each 

 other but lying side by side (Fig. 20, 2. 3. add., Plate 4, Fig. 32), which 

 arise on the dorso-lateral part of the skull, pass forward and downward 

 under the adductors of the mandible, and by means of several slender 

 tendons fuse with the posterior elongation of the chitinous expansion 

 just described (Fig. 20, exp.). I believe their function is, in co-operation 

 with muscles Nos. 4 and 7, to adduct the head of the maxilla. In Figure 

 20, muscles 2 and 3 are represented as interrupted, in order to show cer- 

 tain underlying muscles. 



4. Adductor. A stout muscle (Fig. 20, 4. add.), which arises on the 

 most anterior surface of the cardo, passes forward and is inserted on the 

 ventral surface of the chitinous expansion. 



5. Protrusor and adductor. A slender muscle (Fig. 20, 5. pr^t. add.), 

 which begins on the side of the tentorium, goes outward and somewhat 

 backward, and is attached to the anterior concavity of the cardo, just 

 beneath the insertion of muscle No. 1 . 



6. Protrusor and adductor. Similar to the last in origin and direction, 

 but more ventral and anterior in position (Fig. 20, 6. prt. add.) and in- 

 serted on the most anterior surface of the cardo, just under the insertion 



