THE NERVES. 417 



667. Plexus sacralis s. ischiadicus, 



formed of the first, second and third sacral nerves, and of branches 

 of the fourth and fifth abdominal [lumbar] nerves ; is situated in a 

 direction downwards and outwards towards the inferior extremity 

 of the incisura ischiadica major before the m. pyriformis ; before 

 it, the vasa hypogastrica, which separate it from the peritoneum 

 and rectum. It is connected above with the lumbar plexus [by 

 lumbO'Sacral nerve], in front with the hypogastric plexus; below 

 it continues into the n. ischiadicus, and with the smaller portion of 

 the muscular nerves of the glutseus, the posterior region of the 

 thigh, and into the pudendal nerves. 



1. The secondary branches. 



a. Nn. Itcemorrhoidaks medii and vesicates inferwres, are three 

 or four twigs of the anterior branches of the third sacral nerves, 

 they give branches to plexus hypogastricus (see n. sympathic.),$3iss 

 to the rectum and above the vesiculce seminales to the neck of the 

 bladder, in the female as far as the vagina. 



b. Nn. hcemorrhoidales inferior es, the terminal filaments of the 

 anterior branches of the fourth sacral nerve. This last gives 

 branches to plex. hypogastricus, the prostata, vagina, m. levator 

 ani and coccygeus. 



1. N. glutceus superior, arises from the loops of the third and 

 fourth lumbar with the first sacral nerve, passes above m. pyriformis 

 with art. glutcea through the incisura ischiad. major, anastomoses 

 with the ischiadic nerve, and divides immediately into two or three 

 principal branches, the largest of which passes in a curve to the 

 outer part of the thigh, between glutceus medius and minimus ; it 

 supplies the glutcei [g. med. and minJ\ and skin [?], the tensor 

 fascice, and in the pelvis, the pyriformis. 



2. N. glutceus inferior, arises from the loops of the fourth and 

 fifth lumbar, and first and second sacral nerves, passes out below 

 m. pyriform. with art. ischiadica from incisura -major on the in- 

 ternal surface of glutceus maximus ; ramifies in it and in the skin, 

 and unites with the ischiadic nerve. 



3. N. cutaneus femoris posterior communis, arises from th 

 first and second loop of the sacral nerves, passes out under m. 

 pyriform. through incisura major with art. ischiadica and down- 

 wards between tuber ischii and trocJianter major, dividing into 

 several branches : 



a. Nn. cutanei clunium inferiores are reflected around the in- 

 ferior border of glutceus maximus, supplying the skin of 

 trochanter major and the lower part of the glutseal region. 

 27 



