74 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



hinge is generally on the proximal of the two articulating segments. 

 The coxo-trochanteral joint is always dicondylic. In the telopodite, 

 dicondylic hinges are characteristic of the legs of adult insects, mono- 

 condylic are usual in the legs of larvae (fig. 32 A), but in the larvae 

 of Neuroptera and Trichoptera, the femero-tibial joint is dicondylic. 

 An occasional special, or perhaps generalized, type of hinge consists 

 of a flexible chitinous bar continuous from one segment to the other. 



The Coxa. — In its most symmetrical form, the coxa has the shape 

 of a short cylinder or truncate cone (fig. 31 A, Cx, fig. 33 A). Its 

 proximal end is girdled by a submarginal hasicostal suture (be), 

 which forms internally a low, circular ridge, or basic osta (fig. 33 A, 

 Be), and sets oflf a marginal flange, or basieoxite (Bex), termed the 

 coxomarginale by Crampton and Hasey (1915). The basicosta 

 strengthens the base of the coxa, and serves also for the attachment of 

 some of the coxal muscles. On the mesal half of the coxa, the 

 basicosta is usually weak and often confluent with the coxal margin ; 

 on the outer surface, however, it commonly forms a strong ridge, 

 (%• 33 B, Be), and in some cases a wide ledge (C) upon which 

 muscles of this region are attached (fig, 37 B). The trochanteral 

 muscles that arise within the coxa are attached distal to the basicosta 

 (%• 35 A). 



The coxa has three constant articular surfaces, one proximal on 

 the outer margin of its base (fig. ^3 A, b) articulating with the 

 coxal process of the pleuron, and two distal, one anterior (e) and 

 the other posterior (/), by which the trochanter is hinged to the 

 coxa. The pleural articular surface (b) is formed by an inflection of 

 the wall of the basieoxite, and is supported on the basicosta (fig. 33 B, 

 C). Besides these articulations, there is usually an anterior basal 

 articulation with the ventral extremity of the trochantin (fig. 31 A, 

 a), if the trochantin is present; when the trochantin is absent, there 

 is sometimes a ventral articulation between the coxa and the furci- 

 sternum (fig, 18 I, c). 



The walls of the coxa are often strengthened by internal ridges, 

 the lines of which appear as sutures on the external surface. One 

 ridge extending from the basicosta to the anterior trochantinal articu- 

 lation, marked externally by a corresponding suture (fig. 33 A, d) 

 is more constant than the others, though the position of its proximal 

 end varies. In the legs of centipedes (fig. 32 B) and of caterpillars 

 (A) it extends basally to the middle of the anterior margin of the 

 coxal base. In the fore leg of a grasshopper (fig. 33 D, d) the ridge 

 has a similar position, ending at the articulation of the trochantin 



