86 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8 1 



of the base of the appendage on a single dorsal point of articula- 

 tion (a). 



The adductor fibers of the mandible may all retain their connection 

 with the sternal, or hypopharyngeal, apophyses (Chilopoda, fig. 21 B), 

 or they may become detached from the apophyses and united with the 

 fibers from the opposite jaw to form a transverse dumb-bell muscle 

 (Diplopoda, fig. 26, A, KL; some Crustacea, fig. 27 A, B ; most 

 Apterygota, fig, 27 C, D, KLk), though at the same time some of 

 the fibers may retain their connections with the apophyses, or with 

 the tentorium (Apterygota, fig. 27 C, D, KLt; Orthoptera, fig. 29 C, 

 KLt) or with the base of the hypopharynx (Lepisma, fig. 29 B, KLh ; 

 Locusta, fig. 29 C, KLh ; Microcentrum, fig. 20 D, KLh ; ephemerid 

 nymph, fig. 20 A, KLh). The evolution of the mandibular muscles in 

 the higher insects has been detailed in an earlier paragraph, wherein it 

 was shown that the ventral adductors are reduced and finally obliterated 

 after the jaw has acquired a double hinge with the edge of the cranium, 

 and that the tergal promotor and remotor muscles then become respec- 

 tively the functional abductors and adductors. 



The basal musculature of the insect maxilla, as already shown, 

 coincides almost exactly with the basal musculature of the mandible 

 of a diplopod or a chilopod, and may be derived from the simple plan 

 of the musculature of the annelid parapodium. The tergal promotor 

 is evidently separated into two groups of fibers inserted on the dorsal 

 and ventral extremities of the anterior rim of the appendage base, 

 the upper set being the muscle of the cardo (figs. 25 C, 30 B, 7), the 

 lower set the cranial flexor of the lacinia {Hcc). A tergal remotor is 

 lacking in the insect maxilla, but so it appears to be also in the diplopod 

 mandible (fig. 26 A). The sternal promotor and remotor muscles (figs. 



33 D, E, 35 B, i<^, L) are united, as in the mandible, to form a ventral 

 adductor (KL), the fibers of which almost always retain their origin 

 on the hypopharyngeal apophyses, or on the corresponding part of 

 the tentorium, and are distributed to both the cardo and the stipes 

 (figs. 25 C, 30 B, KLcd, KLst) . In Machilis the maxillary adductors 

 from opposite appendages are united with each other medially, and 

 appear to be detached from the ventral apophyses. 



The margin of the basal cavity of the maxilla (fig. 35 A) includes 

 the region of the cardo, the stipes, and the lacinia ; and the tergal 

 and sternal muscles (/, /, KL) of the appendage are distributed to 

 these three parts. The entire base of the maxilla, therefore, has the 

 fundamental character of a single segment, and there can be no doubt 

 that this segment is the true primitive base of the appendage (fig. 



34 A, LB) . The base of a leg appendage may be divided into a coxa 



