6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO7 



The adductors of the coxa are : ( i ) Muscles that originate on the 

 tergum and insert on an apodemal tendon arising from the medial 

 edge of the first plate of the trochantin, close to the coxo-trochantinal 

 articulation. Present in the three segments. (2) Muscles that origi- 

 nate on the anterior edge of the first plate of the episternum (lEps) 

 and insert along the surface and the anterior edge of the first plate of 

 the trochantin (iTn). Missing in the prothorax. 



The adductors of the coxa have no antagonistic set of abductor 

 muscles, the elasticity of the sclerites being apparently the only force 

 responsible for the abductory movements. 



The rotators of the coxa may be supposed to include the following 

 muscles, though it cannot be determined whether these muscles ac- 

 tually function as rotators or as adductors. They probably perform 

 both movements. ( i ) In the prothorax, a muscle going from the 

 mesothoracic episternum of the opposite side of the body, to the meron 

 (p7 in fig. 54), and another muscle with the same insertion which 

 originates on the first spina (p8 in fig, 54). (2) In the mesothorax, 

 a muscle going from the end of the sternal arm to the ridge which 

 limits the meron in the anterior wall of the coxa ( /j ? in fig. 25 ) , and 

 another muscle that originates on the second spina and inserts on a 

 lower portion of the same ridge (134 in figs. 25 and 30). (3) In 

 the metathorax, two muscles that have their origin on different parts 

 of the sternal arm and insert on different parts of the ridge that limits 

 the meron on the anterior wall of the coxa. (4) In the mesothorax 

 and metathorax, muscles going from the spina to the middle of the an- 

 terior wall of the coxa {10^ and z/j in fig. 54). 



Trochanteral muscles. — The function of the trochanteral muscles is 

 much easier to interpret than that of the coxal muscles. The trochan- 

 ter has, roughl}', the form of a boat, hanging from the coxa by 

 two articulations placed on the opposite sides. From the distal side of 

 the trochanter arises the femur. If we trace a line between the two 

 articular points, it divides the trochanter into a proximal side and a 

 distal (femoral) side. All the muscles inserted on the proximal side 

 will be depressors of the leg; those on the other side, levators. Figure 

 53 represents the trochanter of the right hind leg, seen from the coxal 

 side. The base of the femur can be seen on the upper part of the 

 figure. The line A-A' is the articular line. 180, 181, 182 are the ten- 

 dons of the levators of the leg ; ly/, 1^8, //p those of the depressors. 

 The tendons of the middle leg follow exactly the same arrangement 

 (see fig. 30). The fore legs show a slight variation with only two 

 levators instead of three. 



