542 DISSECTION OF THE PELVIS. 



bladder ; near the external aperture is a hollow in the floor. In conse- 

 quence of not being surrounded by resistant structures, the female urethra 

 is much more dilatable than the corresponding passage in the male. 



Structure. Like the urethra of the male, it consists of a mucous coat, 

 which is enveloped by a plexus of bloodvessels, and by muscular fibre. 



The muscular layer extends the whole length of the urethra. Its fibres 

 are circular, corresponding with the prostatic enlargement in the other sex, 

 and continuous behind with the middle layer of the bladder. In the peri- 

 neal ligament this stratum is covered by the constrictor urethrae as in the 

 male (p. 403). 



The mucous coat is pale except near the outer orifice. It is marked by 

 longitudinal folds; and one of these, in the floor of the canal, resembles 

 the median crest- in the male urethra (p. 526). Around the outer orifice 

 are some mucous follicles ; and towards the inner end are tubular mucous 

 glands, whose apertures are arranged in lines between the folds of the 

 membrane. A laminar epithelium is spread over the surface, and beneath 

 it are deeper conical cells as in the bladder. 



A sub mucous stratum of longitudinal elastic and muscular tissues lies 

 close beneath the mucous membrane, as in the male. 



Dissection. The rectum may be prepared for examination by distend- 

 ing it with tow, and by removing the peritoneal covering and the areolar 

 tissue from its surface. 



RECTUM. The structure of the rectum is similar in the two sexes ; and 

 the student may use the description in the Section on the viscera of the 

 male pelvis (p. 522). 



SECTION VII. 



INTERNAL MUSCLES OF THE PELVIS. 



Two muscles, the pyriformis and obturator internus, have their origin 

 within the cavity of the pelvis. 



Dissection. Take away any fascia or areolar tissue which may remain 

 on the muscles ; and define their exit from the pelvis, the pyriformis pass- 

 ing through the great sacro-sciatic notch, and the obturator through the 

 small notch of the same name. On the right side the dissector may look 

 to the attachment of the levator ani muscle to the pubic part of the hip- 

 bone. 



The PYRIFORMIS MUSCLE is directed outwards through the great sacro- 

 sciatic notch to the great trochanter of the femur. The muscle has re- 

 ceived its name from its form. 



In the pelvis the pyriformis arises by three slips from the second, 

 third, and fourth pieces of the sacrum, between the anterior aperture.-, 

 and from the lateral part of the bone external to those holes ; as it passes 

 from the pelvis, it takes origin also from the surface of the hip-bone form- 

 ing the upper part of the large sacro-sciatic notch, and from the great 

 sacro-sciatic lig.iment. From this origin the fibres converge to the ten- 

 don of insertion into the trochanter. (Dissection of the B.ittock.) 



The anterior surface is in contact with the rectum on the left side, with 

 the sacral plexus, and with the sciatic and pudic brandies of the internal 



