THE MUSCLES AND FASCIA OF THE PELVIS 



421 





the Obturator interims and are enclosed in a special canal Alcock's canal 

 formed by the obturator fascia. 



The fascia of the Piriformis is very thin and is attached to the front of the sacrum 

 and the sides of the greater sciatic foramen; it is prolonged on the muscle into 

 the gluteal region. At its sacral attachment around the margins of the anterior 

 sacral foramina it conies into intimate association with and ensheathes the 

 nerves emerging from these foramina. Hence the sacral nerves are frequently 

 described as lying behind the fascia. The internal iliac vessels and their branches, 

 on the other hand, lie in the subperitoneal tissue in front of the fascia, and the 

 branches to the gluteal region emerge in special sheaths of this tissue, above and 

 below the Piriformis muscle. 



[ Superior L5 



Diaphragmatic i ayer I 

 part of pelvic J s. 



fascia Inferior 



\_ layer 



Tendinous arch 



i 



Fascia endopelvina , 

 Vesicula seminalie 



Ductus deferens 

 Rectovesical layer 



\ 



Fio. 402. Coronal section of pelvis, showing arrangement of fasciae. Viewed from behind. (Diagrammatic.) 



The diaphragmatic part of the pelvic fascia (Fig. 402) covers both surfaces of the 

 Levatores ani. The inferior layer is known as the anal fascia; it is attached above 

 to the obturator fascia along the line of origin of the Levator ani, while below it 

 is continuous with the superior fascia of the urogenital diaphragm, and with the 

 fascia on the Sphincter ani internus. The layer covering the upper surface of the 

 pelvic diaphragm follows, above, the line of origin of the Levator ani and is there- 

 fore somewhat variable. In front it is attached to the back of the symphysis 

 pubis about 2 cm. above its lower border. It can then be traced laterally across 

 the back of the superior ramus of the pubis for a distance of about 1.25 cm., when 

 it reaches the obturator fascia. It is attached to this fascia along a line which 

 pursues a somewhat irregular course to the spine of the ischium. The irregularity 

 of this line is due to the fact that the origin of the Levator ani, which in lower 

 forms is from the pelvic brim, is in man lower down, on the obturator fascia. 

 Tendinous fibers of origin of the muscle are therefore often found extending up 

 toward, and in some cases reaching, the pelvic brim, and on these the fascia is 

 carried. 



It will be evident that the fascia covering that part of the Obturator internus 

 which lies above the origin of the Levator ani is a composite fascia and includes 

 the following: (a) the obturator fascia; (6) the fascia of the Levator ani; (c) 

 degenerated fibers of origin of the Levator ani. 



