210 ANATOMY OF THE ABDOMEN, ETC. 



veins, which, with the exception of the hemorrhoidal am 

 spermatic veins, empty into the internal iliac vein. The 

 hemorrhoidal veins, more or less connected with the othei 

 veins, especially those about the neck of the bladder, empti 

 into the inferior mesenteric vein, which terminates in the 

 vena portae. It will thus be seen that constipation, or any 

 cause which obstructs the circulation of the vena portae 

 will also arrest the blood in the hemorrhoidal veins, and 

 so give rise to the condition known as piles or hemorrhoids. 

 The spermatic and ovarian veins terminate, the right in 

 the vena cava, the left in the renal vein. 



The nerves of the pelvic cavity are numerous, important, 

 and many of them of large size. 



The lumbo-sacral and obturator nerves have been already 

 described (p. 200) ; they are again seen at this stage of the 

 dissection, the former joining the sacral plexus, the latter 

 passing out at the obturator foramen with the obturator 

 artery. 



The SACRAL PLEXUS is formed from the four anterior 

 sacral nerves. The fifth sacral nerve terminates in the 

 perineum, where it unites with the sixth, or coccygeal 

 nerve, and is distributed to the side of the coccj'x and 

 coccygeus muscle. The sacral plexus is a broad, flat, 

 nervous band lying upon the pyriformis muscle ; w T ithin 

 the pelvis, it furnishes several visceral branches to the 

 pelvic organs, which unite with the branches of the hypo- 

 gastric plexus, and also muscular branches to the internal 

 pelvic muscles; it then divides into the following branches, 

 destined to external parts, viz : 



Gluteal, 

 Internal Pudic, 

 Great Sciatic, 

 Lesser Sciatic. 



These all pass out through the greater sacro-ischiatic 

 foramen, and will be described in connection with the parts 

 to M'hich they are distributed. 



The pelvic fascia, covering in the obturator internus 

 muscle, may be traced as a single layer from the brim of 

 the pelvis as far as a white, tendinous line stretching from 

 the symphysis pubes to the spine of the ischium ; at this 

 line it divides into two layers, one of which continues over 

 the rest of the obturator muscle, and the other, under the 

 name of the recto-vesical fascia, passes clown to be attached 



