I330 HUMAN ANATOMY. 



internus and the adductor magnus. At the inner side of the knee it becomes superficial by 

 passing between the tendons of the sartorius and gracilis and by piercing the deep fascia in this 

 situation. Thence it descends in the leg in association with the internal saphenous vein, at the 

 ankle passing anterior to the internal malleolus and reaching the inner aspect of the foot, on 

 which it extends only as far as the metacarpo-phalangeal articulation of the great toe (Fig. iiiS). 



Branches of the internal saphenous are : the coimmcnicating , the infrapatellar, the articu- 

 lar and the terminal. 



The coymnnni eating branch arises beneath the sartorius at about the middle of the thigh 

 and inosculates with filaments from the obturator and internal cutaneous nerves to form the 

 sub sartorial ox obturator plexus. 



The infrapatellar branch (r. infrapatellaris) (Fig. 1117) arises at the lower part of the 

 thigh. It perforates the sartorius and the fascia lata and spreads out beneath the integument 

 of the knee, where it inosculates with terminal filaments of the internal, the middle and some- 

 times the external cutaneous nerve to form i\\Q patellar plexus (Fig. 11 17). 



The articular branch (r. articularis) is an inconstant twig which supplies the inner portion 

 of the capsule of the knee joint. 



The terniifial branches are distributed to the integument of the anterior internal portion 

 of the leg and the posterior half of the dorsum and mesial side of the foot. 



Practical Considerations. — All the branches of the lumbar plexus have motor 

 and sensory fibres, both of which are affected in paralysis. The lesion is usually 

 central, involving the spinal cord, as in tabes dorsalis, fracture of the spine or Pott's 

 disease, and involves several nerves, or all of them below the seat of the lesion ; the 

 individual branches are not often affected. 



The ilio-hypogastric may be divided by the incision in kidney operations or 

 may be included in the sutures. This nerve and the ilio-ingicinal are sometimes 

 involved in operations in the inguinal region. 



The genito-crural sends one branch through the inguinal canal to the cremaster 

 muscle, and another under Poupart's ligament to the skin of the inner side of the 

 thigh, just below the ligament. Gentle irritation of the skin here will cause retraction 

 of the testicle (cremaster reflex), especially in children. 



The anterior crural has been paralyzed by the pressure of tumors in the pelvis, 

 has been involved in a psoas abscess, and has been injured in fracture of the pubic 

 ramus and — rarely — in fractures of the femur. If the lesion involving the nerve is 

 within the pelvis the paralysis would af?ect the ilio-psoas, quadriceps extensor femoris, 

 sartorius and pectineus. If the lesion is outside the abdomen the ilio-psoas will 

 escape. A complete paralysis would prevent flexion of the hip, or extension of the 

 knee. The patient is then compelled to avoid flexion of the knee in walking. There 

 will be anesthesia in the parts supplied by the middle and internal cutaneous, and 

 long saphenous nerves, that is, in the thigh along the anterior and inner surface 

 (middle and internal cutaneous), except in the upper third (crural branch of the 

 genito-crural), and along the inner surface of the leg and inner border of the foot to 

 the ball of the big toe (long saphenous). The long saphenous vein and nerve lie 

 close together, about a finger's breadth behind the inner border of the tibia. In the 

 thigh, while they have the same general direction, the vein lies in the superficial 

 fascia, the nerve under the deep fascia. The nerve in the thigh is, therefore, not so 

 liable to injury as is the vein. 



Since the anterior crural breaks up into numerous branches just below Poupart's 

 ligament, its trunk in the thigh is very short. It lies slightly external to the femoral 

 artery and can be exposed by an incision extending downward from the middle of 

 Poupart's ligament. 



Paralysis of the obturator ney've would interfere with adduction of the thigh as 

 well as with internal and external rotation. It may be caused by pressure within the 

 pelvis, as by the child's head in difhcult labor, by a tumor or by an obturator hernia. 

 Paralysis of the obturator is usually found in conjunction with paralysis of the anterior 

 crural. The nerve may be irritated in coxalgia, in sacro-iliac disease, and on the left 

 side in carcinoma or faecal impaction in the sigmoid flexure. On account of its ter- 

 minal distribution pain in the knee is usually complained of whenever this nerve or 

 one of its branches is involved. 



