72 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



The niesal promotor and the mesal remoter take their origins on 

 the metathoracic basal components of the pterothoracic endosternum 

 (fig. 24 A, 104, 106) ; the lateral promotor (lo^) arises on the ridge 

 between the metapleuron and the propodeum. 



The coxo-trochantcral joint. — The union between the coxa and the 

 trochanter in each leg of the bee is a dicondylic hinge with an ap- 

 proximately horizontal anteroposterior axis. The movements of the 

 trochanter on the coxa, therefore, are up and down, and are best 

 expressed as levatlon and depression. In the bee the trochanter 

 of each leg is provided with two levator muscles, one anterior, the 

 other posterior, arising within the coxa, and with two or three de- 

 pressors having a common point of insertion, but arising both in the 

 coxa and within the thorax. The two levators are inserted directly 

 on the trochanter or close to it ; the fibers of the depressor muscles 

 have no direct connection with the trochanter, but are inserted on a 

 large depressor apodeme arising from a small plate in the ventral 

 articular membrane at the base of the trochanter. The trochanteral 

 muscles are the motors of the entire part of the leg (telopodite) be- 

 yond the coxa, the movements of which are in a plane at right angles 

 to the coxal plane of movement. 



In the fore leg the relatively small anterior and posterior levators 

 of the trochanter (fig. 13 E, H, 59, 60) arising in the coxa are 

 inserted on the trochanteral base just beyond the coxo-trochanteral 

 articulations (E, /, g). The depressors include a long thoracic 

 muscle (E, H, 61) arising on the prothoracic pleural apophysis (figs. 

 II C, 12 C, 61), which is inserted on the end of the depressor apodeme 

 of the trochanter (fig. 13 E, H), and a large group of fibers (62), 

 arising on the mesal wall of the coxa, inserted on the sides of the 

 apodeme and on the apodemal plate. Since the articular surfaces of 

 the trochanter (E, f, g) are much closer to the insertions of the 

 levator muscles than to the base of the depressor apodeme, the 

 effectiveness of the large depressor muscles is greatly increased by 

 their advantageous leverage. 



In the mesothoracic legs the two levator muscles of each trochanter 

 arise on the lower (lateral) wall of the coxa (fig. 22 D, 84, 8j), and 

 are inserted anteriorly and posteriorly on the base of the trochanter. 

 The thoracic muscle of the depressor group (D, G, 86) takes its 

 origin on the side of the endosternum (C) ; the coxal fibers are 

 distinctly divided into two muscles (D, G, 8/, 88), one anterior, the 

 other posterior, separated by the pedal nerve (G, Nv) entering 

 between them into the trochanter. 



