NO. I 



INSECT THORAX — SNODGRASS 



79 



In a few insects the trochanter appears to be double. Tn some of 

 the Hymenoptera (Ichneumonidae, Braconidse), for example, two 

 pieces of the leg occur between the coxa and the femur which are 

 called " first trochanter " and " second trochanter." That the first 

 alone is the trochanter (fig. 35 B, Tr), however, is shown by the 

 fact that the reductor fenioris muscle {R) is inserted on a plate {i) 

 inflected from the base of the second (F'). The latter is, therefore, 

 a basal subsegment of the femur ( F), separated by a secondary suture 



Fig. 35. — Structure and musculature of the coxa, trochanter, and base of femur. 



A, diagram of typical musculature of coxa, trochanter, and base of femur ; 

 B, trochanter and base of femur of an ichneumonid {Mcgaryssa), showing basal 

 subdivision {F') of the femur (F) ; C, trochanter and base of femur of middle 

 leg of dragonfly nymph ( Aeschnidae), showing double structure of the trochanter 

 {iTr, 2Tr). 



Be, basicosta of coxa ; be, basicostal suture ; Bex, basicoxite ; Cx, coxa ; 

 F, femur ; F', basal subdivision of femur ; /. posterior coxo-trochanteral articu- 

 lation; g, basicosta of trochanter; /;, ridge between subdivisions of trochanter; 

 /, basicosta of femur ; /, femoral ridge setting ofl' basal subdivision of femur ; 

 O, levator muscle of trochanter; P, thoracic branch of depressor of trochanter; 

 Q, coxal branch of depressor of trochanter; R, reductor muscle of femur; S, 

 levator of tibia ; T. depressor of tibia ; Tr, trochanter ; iTr, 2Tr, first and second 

 subdivisions of trochanter. 



and ridge ( j) . A branch of the tibial flexor (T) crosses the ridge 

 and is attached at the anterior end of the true femoral base. 



In the Odonata, both nymphs and adults, there appear likewise to 

 be two trochanteral seginents (fig. 35 C, iTr, 2Tr). The structural 

 relations here, however, are quite dififerent from those in the hymen- 

 opteran leg (B). The reductor femoris muscle {R) of the dragon- 

 fly arises in the second trochanter, and the ridge (/) upon which it 

 is inserted is clearly the basicosta of the femur (F). The ridge (//) 

 with its external suture between the two parts of the trochanter is, 

 therefore, a trochanteral structure, and its presence furnishes a 



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