MYOLOGY 75 



its superior tuberosity. It converges sharply to its in- 

 sertion upon the caudal base of the lesser trochanter. It is 

 thus intermediate in position between the obturators ex- 

 ternus and internus. 



The innervation of these five muscles is by branches 

 from the sacral plexus. 



M. obturator externus (figs. 32, 33) has origin from 

 the entire lateral border of the obturator foramen except 

 its extreme cranial portion. Converging, it passes just 

 ventrad of the obturator internus to an insertion deep to 

 the latter and into the trochanteric fossa. 



Innervation of this muscle is by the N. obturatorius. 



B. MUSCLES OF THE THIGH 



The muscles of the thigh consist of flexors, extensors and 

 adductors. 



The flexors number six as follows: 



Mm. semimembranosus anticus biceps femoris anticus 



semimembranosus posticus biceps femoris posticus 



semitendinosus tenuissimus 



The semimembranosus is double, as is so often the case, 

 and one of the slips is probably the most variable muscle 

 in the body. 



M. semimembranosus anticus (figs. 6, 32, 33) is ex- 

 ceedingly variable in its origin. In a selected specimen it 

 arose by two heads. The larger and more superficial of 

 these extended from the fascia investing the sacrocaudal 

 muscles, while the deeper head, but two millimeters in 

 width, arose by tendon fibers from the ischium just craniad 

 of its superior tuberosity. The two heads united im- 

 mediately and the slender muscle resulting passed upon 

 the medial side of the leg, deep to the medial part of the 

 insertion of the adductor femoris, to an insertion upon the 

 tibia just distad of the medial tuberosity. In the four 



