480 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1931 



TTie maxillae. — The first pair of maxillary appendages of insects 

 are usually called " the maxillae," because the second pair are united 

 in the labium. The maxillae in their typical form are the most 

 leglike of the gnathal appendages. The usual structure of a maxilla 

 of biting insects is well illustrated in the maxilla of the cricket, 

 shown in Figure 21 C, which presents the posterior surface of a 

 right appendage. The anterior wall is less complete, because the 

 maxilla is broadly attached by most of the anterior surface of its 

 basal part to the wall of the head. The basis of the appendage is 

 divided into the proximal cardo {Gd) and the distal stipes {St). 

 The stipes bears laterally the long palpus {Pip), and distally the 

 two endite lobes, lacinia (Lc) and galea (Ga). A lobe of the stipes 

 supporting the galea is sometimes distinguished as the suhgalea 

 {sga), and a more or less differentiated lateral lobe bearing the 

 palpus is known as the palpifer {Plf) . The cardo is usually divided 

 externally by the line of a strong internal ridge, and the area of 

 the stipes may also be marked by external grooves, or " sutures," 

 that form internal strengthening ridges. 



The maxilla is always articulated to the hypostomal rim of the 

 cranium by a single point of articulation (fig. 8, a") borne on the 

 base of the cardo (fig. 21 C, a"). It thus preserves the primitive 

 single 'articulation with the head, which corresponds with the primi- 

 tive mandibular articulation (figs. 2 B, 20 A, a'), or with the pos- 

 terior articulation of the mandible in pterygote insects (fig. 20 

 B,a'). 



The musculature of the maxilla is so nearly identical with that 

 described in the last section for a generalized gnathal appendage 

 (fig. 19) that it need not be described in detail here. Usually there 

 are only two maxillary muscles arising on the dorsal part of the 

 cranium, both of which (/) apparently belong to the dorsal pro- 

 motor system of a primitive appendage (fig. 14, /), though they 

 are widely separated on the anterior margin of the maxillary base. 

 One is inserted on the carclo (fig. 19 rfmxa), the other at the basal 

 angle of the lacinia {fl^c) ; the latter functions, therefore, as a 

 cranial flexor of the lacinia. The dorsal remotor {J) is usually 

 lacking, but is sometimes present as a posterior muscle of the cardo. 

 The ventral muscles {KLt) are powerful adductors. They take 

 their origin on the tentorium, and are inserted within both the 

 cardo and the stipes. The intrinsic muscles of the maxilla all arise 

 within the stipes. They comprise a levator and depressor of the 

 palpus (O, Q), a flexor of the galea {fffa), and a stipital flexor of 

 the lacinia {flcs). 



The disposition of the maxillary muscles leaves little doubt that 

 the cardo and stipes are but secondary subdivisions of the primitive 



