14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



of movement in the coxa is always between its dorsal and ventral 

 angles, we may presume that the chilopod coxa has had both a dorsal 

 and a ventral articulation with the subcoxa (fig. i, c, d), though one 

 or the other, or both of the articulations (fig. 8) may lose the struc- 

 ture of definite articulating surfaces. 



In the geophilid Sfrigamia bothriopus (fig. 8) the subcoxal area of 

 the pleuron has the form of a complete basal limb segment (A, Sex), 

 though its ventral margin is expanded and united with the sternum 

 (B), and the coxa turns upon it by an obliquely vertical axis. In 

 Scolopendra, Lithobius (fig. 9), and Sciitigera (fig. 10) the subcoxal 

 area is mostly membranous, but it contains one or more well-sclerotized 

 plates. 



The tergal muscles of the leg bases in the Chilopoda are inserted not 

 on the coxae but on the subcoxae. In Scutigera the tergo-subcoxal 

 muscles are strongly developed, those of each leg comprising a pair 

 of anterior (promotor) muscles (fig. 10 B, /) inserted upon the dorsal 

 plate (coxopleure, cpl) of the subcoxal region, and a single large 

 posterior (remotor) muscle (/) inserted on the posterior dorsal mar- 

 gin of the subcoxal region. 



The structure and musculature of the subcoxal region in the 

 Chilopoda can leave little doubt that this area is the true base of the 

 leg, which has become flattened into the lateral body wall, where, in 

 most forms, its sclerotization has been more or less broken up and 

 reduced. The sternal muscles of the leg base in the chilopods have 

 gone over to the ventral rim of the coxa (fig. 10 B). They include 

 an anterior (ventral promotor) muscle (A') and a posterior (ventral 

 remotor) muscle (L). In Scutigera (fig. 10) the first of these mus- 

 cles arises in the anterior lateral angle of the sternum, but in Scolopen- 

 dra the corresponding muscle arises mesally on the anterior half of 

 the sternum. The fibers of the posterior muscle in Scutigera (fig. 10 B, 

 L) are mostly continuous from one coxa to the other, but a small 

 anterior group on each side arises on the sternum at the base of the 

 ligamentous endosternal furca (Fu). In Scutigera the coxa has no 

 ventral articulation with the subcoxa or the sternum, but in those 

 chilopods in which a ventral subcoxo-coxal articulation is present, the 

 anterior and posterior ventral muscles {K, L) must act as promotors 

 and remotors. 



The base of the coxa in the Chilopoda is provided also with median 

 dorsal and ventral muscle. The dorsal median muscle in Scutigera 

 (fig. 10 B, M) consists of a flat band of short fibers arising on the 

 dorsal plate of the subcoxa {cpl), and is inserted on the rim of the 

 coxa just behind the dorsal articulation with the subcoxa. This muscle 



