THE PUDENDAL PLEXUS 1065 



and Coccygeus enter their pelvic surfaces; that to the Sphincter ani externus 

 (perineal branch) reaches the ischiorectal fossa by piercing the Coccygeus or by 

 passing between it and the Levator ani. Cutaneous branches from this branch 

 supply the skin between the anus and the coccyx. 



Anococcygeal Branches (nn. anococcygei). The fifth sacral nerve receives a 

 communicating branch from the fourth, and unites with the coccygeal nerve to 

 form the coccygeal plexus (plexus coccyyeus). From this plexus the anococcygeal 

 nerves take origin; they consist of a few fine filaments which pierce the great 

 sacrosciatic ligament to supply the skin in the region of the coccyx. 



Applied Anatomy. The lumbar plexus is formed in the Psoas magnus, and, therefore, in 

 Psoas abscess any or all of its branches may be irritated, causing severe pain in the parts to which 

 the irritated nerves are distributed. The genitofemoral nerve is the one which is most frequently 

 implicated. The nerve is also of importance, as it is concerned in one of the reflexes employed 

 in the investigation of diseases of the spine. If the skin over the inner side of the thigh just 

 below Poupart's ligament, the part supplied by the femoral branch of the genitofemoral nerve, 

 be gently tickled in a male child, the testicle will be noticed to be drawn upward through the 

 action of the Cremaster, which is supplied by the genital branch of the same nerve. The same 

 result may sometimes be noticed in adults, and can almost always be produced by severe stimu- 

 lation. This reflex, when present, shows that the portion of the cord from which the first and 

 second lumbar nerves are derived is in a normal condition. 



The femoral or anterior crural nerve is in danger of being injured in fractures of the true pelvis, 

 since the fracture most commonly takes place through the ascending ramus of the os pubis, at or 

 near the point where this nerve crosses the bone. It is also liable to be injured in fractures and 

 dislocations of the femur, and in some tumors growing in the pelvis is likely to be pressed upon, 

 and its functions impaired. Moreover, on account of its superficial position, it is exposed to 

 injury in wounds and stabs in the groin. When this nerve is paralyzed, the patient is unable to flex 

 his hip completely, on account of the loss of motion in the Iliacus; or to extend the knee on the 

 thigh, on account of paralysis of the Quadriceps extensor cruris; there are complete paralysis of 

 the- Sartorious and partial paralysis of the Pectineus. There is loss of sensation down the front and 

 inner side of the thigh, except in that part supplied by the femoral branch of the genitofemoral 

 nerve, and by the ilioinguinal nerve. There is also loss of sensation down the inner side of the 

 leg and foot as far as the ball of the great toe. 



The obturator nerve is of special surgical interest. It is rarely paralyzed alone, but occa- 

 sionally is paralyzed in association with the femoral (anterior crural). The principal interest 

 attached to it is in connection with its supply to the knee; pain in the knee being symptomatic 

 of many diseases in which the trunk of this nerve, or one of its branches, is irritated, Thus, it is 

 well known that in the earlier stages of hiv-jw'' fftyjr""' * KQ patient does not complain of pain in 

 that articulation, bjjt_on_the inner side of tneknee. or in the knee-joint itself, both these artlcu- 

 lations being supplied~By the obturator nerve, the final distribution of the nerve being to the 

 knee-joint. Again, the same thing occurs in sacroiliac disease: pain is complained of in the 

 knee-joint or on its inner side. The obturator nerve is in close relationship with the, sacroiliac 

 articulation, passing over it, and, according to some anatomists, distributing filaments to it. 

 Again, in cancer of the sigmaid flexure, and even in cases where masses of hardened feces are 

 impacted in this portion of the gut, pain is complained of in the knee. The left obturator nerve 

 lies beneath the sigmoid flexure, and is readily pressed upon and irritated when disease exists in 

 this part of the intestine. Finally, pain in the knee forms an important diagnostic sign in ob- 

 turator hernia. The hernial protrusion as it passes through the opening in the obturator mem- 

 brane presses upon the nerve and causes pain in the parts supplied by its peripheral filaments. 

 When the obturator nerve is paralyzed, the patient is. unable to press his knees together or to 

 cross one leg over the other, on account of paralysis of the Adductor muscles. Rotation outward 

 of the thigh is impaired from paralysis of the Obturator externus. Sometimes there is loss of 

 sensation in the upper half of the inner side of the thigh. 



The great sciatic nerve is liable to be pressed upon by various pelvic tumors, giving rise to 

 pain along its trunk, to which the term sciatica is applied. Tumors growing from the pelvic 

 viscera, or bones, aneurisms of some of the branches of the internal iliac artery, calculus in the 

 bladder, when of large size, accumulation of feces in the rectum, may all cause pressure on the 

 nerve inside the pelvis, and give rise to sciatica. Outside the pelvis exposure to cold, violent 

 movements of the hip-joint, exostoses or other tumors, growing from the margin of the sacro- 

 sciatic foramen, may also give rise to the same condition. When paralyzed there is loss of 

 motion in all the muscles below the knee, and loss of sensation in the same situation, except the 

 upper half of the back of the leg, supplied by the small sciatic and the upper half of the inner 

 side of the leg, when the communicating branch of the obturator is large. 



The great sciatic nerve has been frequently cut down upon and stretched, or has been acu- 



