840 A MANUAL OF ANATOMY 



side of the middle line. These fibres constitute the so-called 

 ■picbo-vesical muscles. 



Anal Fascia. — ^This very thin sheet of fascia is an offshoot from 

 the parietal pelvic fascia just below the white line and the origin 

 of the levator ani. It closely covers the ischio-rectal surface of 

 that muscle and of the coccygeus, upon which it descends to the 

 region of the anus, where it blends with the aponeurotic investment 

 of the sphincter ani externus. 



Sympathetic Plexuses in the Pelvis. — ^These are derived from 

 the hypogastric plexus, which is formed by the fusion of the two 

 lateral strands of the aortic plexus after they have crossed the 

 common iliac arteries. It is reinforced by branches from the 

 ganglia of the lumbar sympathetic cords, and is situated in front 

 of the body of the fifth lumbar vertebra between the common iliac 

 vessels. It is a large, flattened plexus, measuring about i| inches 

 in breadth, and it breaks up into two divisions, which form the right 

 and left pelvic plexuses. Each of these enters the pelvis on the 

 inner side of the internal iliac artery, and takes up a position on 

 the side of the rectum. The pelvic plexus of each side is reinforced 

 by branches from the upper one or two ganglia of the pelvic sym- 

 pathetic chain, and by spinal fibres from the anterior primary 

 divisions of the third and fourth sacral nerves (sometimes also the 

 second), therKJbeing very small ganglia at the places of junction. 

 From each plexus the following secondary plexuses are given off, 

 which accompany the corresponding branches of the internal iliac 

 artery : hemorrhoidal, vesical, prostatic, vesicular, and deferential, 

 the latter three being replaced in the female by the vaginal and 

 uterine plexuses. 



Internal Iliac Artery. — ^This vessel arises from the common iliac 

 opposite the lumbo-sacral articulation, and terminates opposite 

 the upper border of the great sciatic notch by dividing into an 

 anterior and a posterior division. The length of the vessel is about 

 i| inches, and its direction is downwards and backwards. 



Relations — Anterior. — ^The artery is covered by the peritoneum, 

 and the ureter descends over it. The terminal part of the ileum 

 forms an anterior relation of the right vessel, whilst the pelvic 

 colon is similarly related to the left. Posterior. — ^The vessel rests 

 chiefly upon its own vein, but near its origin it is placed over the 

 commencement of the common iliac vein. Behind the veins there 

 are the lumbo-sacral cord and ala of the sacrum. External. — ^The 

 psoas magnus, with the intervention of the external iliac vein, and 

 subsequently the lateral wall of the pelvis, with the intervention 

 of the obturator nerve. Internal. — ^The peritoneum. 



Varieties. — ^Ihe chief variety affects the length of the vessel. It may be 

 shorter or longer than usual, according as the common iliac is longer or shorter 

 than normal, or according to the height at which the internal iUac ends in its 

 two divisions. 



Foetal Condition. — During foetal life the internal iliac is represented by the 

 hypogastric and umbilical arteries, the size of which greatly exceeds that of 

 the external iliac. The function of these arteries is to carry the impure blood 



