1 62 TOPOGRAPHIC AND APPLIED ANATOMY. 



the gluteofemoral crease does not correspond with the inferior margin of the gluteus maximus, 

 but that it is situated from two to three fingerbreadths above this margin. In its further course 

 the sciatic nerve passes beneath the muscles arising from the tuberosity of the ischium, disappear- 

 ing beneath the biceps, and runs downward in the middle of the posterior surface of the thigh, 

 covered by the long head of the biceps, to reach the popliteal space. Anteriorly the nerve rests 

 upon the adductor magnus muscle. It is surrounded by very loose connective tissue in which 

 gravitating abscesses leaving the pelvis through the sciatic foramina may extend downward 

 along the nerve into the popliteal space. The nerve may divide high up into its two terminal 

 branches, the internal and the external popliteal nerves; the point of division is usually situated 

 just above the popliteal fossa (Fig. 83). The nerve supplies the long head of the biceps, the 

 semimembranosus, and the semitendinosus from the portion which subsequently becomes the 

 internal popliteal nerve, and the short head of the biceps from the portion which goes to form 

 the external popliteal nerve. The sciatic nerve also gives filaments to the adductor magnus 

 muscle. 



Obturator Nerve. The obturator nerve (Figs. 71 and 73), the motor nerve of the adductors 

 and the last branch of the lumbar plexus, runs into the true pelvis to the inner side of the psoas 

 muscle, and, accompanied by the obturator artery, to the obturator canal, and divides, after its 

 exit from the canal, into an anterior and a posterior branch. The anterior branch lies between 

 the adductor brevis upon one side and the pectineus and the adductor longus upon the other; 

 it supplies these muscles and the gracilis and ends in an unimportant cutaneous branch upon the 

 inner side of the thigh (Fig. 79). The posterior branch lies beneath the adductor brevis and 

 upon the adductor magnus and supplies the latter muscle. 



THE REGION OF THE KNEE. 



In the region of the knee may be easily seen and felt the movable patella, imbedded in the 

 tendon of the quadriceps and covered only by the skin and bursas (see page 165), and the liga- 

 mentum patella, which passes from the apex of the bone to the tubercle of the tibia. To either 

 side may be felt the condyles and the epicondyles of the femur. When the knee is flexed, the 

 patella descends so that the upper portion of the intercondyloid fossa of the femur (the trochlea) 

 is exposed to palpation. To the outer side of the extended knee a strong band may be distinctly 

 felt passing upward from the external epicondyle; this structure is the terminal portion of the 

 iliotibial band of the fascia lata. To either side of the patellar tendon may be felt the articular 

 space between the tibia and the femur, and, upon the outer side of the joint, the head of the 

 fibula and the strong tendon of the biceps which passes upward from this structure. [On either 

 side of the patella and above it are depressions; these, with the depressions on either side of the 

 patellar ligament, disappear when there is fluid in the joint cavity. When fluid is present, the 

 patella "floats"; which means that by pressure backward the patella may be forced in contact 

 with the femur, but when the pressure is released it rebounds. ED.] When the knee is flexed, the 

 biceps tendon may be followed upward upon the posterior surface of the thigh. It forms the 

 outer boundary of the upper portion of the popliteal fossa, the inner boundary being furnished 

 by the tendons of the semitendinosus, semimembranosus, and gracilis. The lower portion of 

 the diamond-shaped popliteal fossa is bounded by the origins of the gastrocnemius muscle. 



