ABDOMINAL SPINAL NERVES. 507 



which, it divides into an anterior and posterior branch. The 

 first is distributed to the head of the adductor longus and bre- 

 vis, and to the gracilis and integuments. The second terminates 

 in the obturator externus, and the adductor magnus. 



The Sciatic Plexus (Plexus Ischiadicus) is formed by the union 

 of the last lumbar with tbe four upper sacral nerves; the last 

 lumbar, before it joins the plexus, receiving the branch of the 

 fourth lumbar nerve, which is left after the lumbar plexus is 

 formed. This plexus is situated at the side of the rectum be- 

 fore the pyriformis muscle. 



The volume of the posterior branches of the Sacral Nerves 

 increases till the fourth; but the fifth and the sixth are much 

 smaller, in fact only fibrillse. 



The anterior branches of the sacral nerves are much larger 

 than the posterior. The four first communicate with the sacral 

 ganglions of the great sympathetic, besides forming the ischi- 

 atic plexus. They assist the sympathetic, to form the hypo- 

 gastric plexus. The fifth, and the sixth, when it exists, are dis- 

 tributed to the coccygeus, sphincter, and levator ani.* 



The following small branches go from the Sciatic Plexus.f 



a. Nervi Glutcei: one passes through the upper part of the 

 sciatic notch along with the artery, to the glutseus rnedius and- 

 minimus; another below the pyriformis muscle to the glutaeus 

 magnus. 



b. Nervus Pudendalis Longus Inferior, passes under the tu- 

 ber of the ischium to the glutaeus magnus; perineal muscles; 

 urethra and integuments of the penis and scrotum in men; and 

 to the inferior parts of the labium externum in women. 



c. Ramus Femoralis Cutaneus Posterior. This nerve is 

 placed between the integuments of the thigh and the muscles 

 which arise from the tuberosity of the ischium. It sends many 

 branches, successively, to the skin on the back of the thigh; 

 one of its branches, longer than the others, goes down to the 



* This is only given as the most frequent arrangement of the sciatic plexus, 

 and of the branches of nerves which proceed from it; other arrangements will 

 often be met with in the cavity of the pelvis, in which not so many sacral nerves 

 are sent to the plexus ischiadicus, and the several branches proceeding from it de- 

 part in a different manner. 



f They sometimes come from a common trunk, called, in such case, the Small 

 Sciatic. 



