NO. I 



INSECT THORAX — SNODGRASS 



75 



(Til) with the coxa. This position suggests that the ridge may be 

 a primitive coxal structure forming a brace between the anterior 

 trochantinal and trochanteral articulations. In many cases, however, 

 the ridge extends basally to the pleural articulation (fig. 33 A, d'), 



Fig. ss. — Structure of the coxa. 



A, diagram of coxal structure, lateral view, showing marginal basicoxitc 

 (Bex) separated from body of coxa by internal basicostal ridge (Be) and ex- 

 ternal basicostal suture (be) : b, pleural articulation; d, d', varying positions of 

 anterior coxal suture ; c, f, anterior and posterior trochanteral articulations. 



B, basal part of external wall of coxa, inner surface: showing pleural articu- 

 lation (b) supported on basicosta (Be). 



C, same parts of a coxa with part of basicoxite posterior to pleural articula- 

 tion (h) enlarged to form the basal coxal lobe known as the meron (Mcr). 



D, base of fore leg of grasshopper (Dissosfcira) : anterior suture (d) ex- 

 tending between trochantinal and trochanteral articulations. 



E, middle leg of same; anterior suture (d') continuous above with pleural 

 suture (PIS). 



F, base of right middle coxa and associated pleural parts, inner view, of 

 cicada (Tibicina scptendccim) : showing point of attachment of promotor muscle 

 (/) on trochantin (Tii), and of remotor (/) on meron (Mcr). 



G, middle coxa of peach borer moth (Aegaria e.ritiosa) : meron (Mer) 

 greatly enlarged ; anterior suture (d) partly suppressed. 



H, Diagram of coxal structure with meron (Mcr) extended distally, and 

 anterior suture (A, d) lacking. 



as in the middle leg of a grasshopper (E, d'), and its suture then falls 

 in line with the pleural suture (PIS). The latter condition has given 

 rise to the idea that the coxa is formed of an anterior and a posterior 

 part corresponding with the episternum and the epimeron, but it is 

 clear that this conception is based on a superficial character, which 

 is also a variable one. The coxal ridge is sometimes incomplete basally 



