DISSECTION OF THE PELVIS. 357 



sphincter ani externus and the retractor ani. These are described at 

 page 284. In the male the retractor muscles of the penis (page 284) 

 form a kind of sling for the rectum in front of the anus ; and similar 

 cords of involuntary muscular tissue unite below the rectum at the 

 same point in the female, and terminate in the vulva. 



The Urinary Bladder (Plates 46 and 47) is the reservoir for the 

 accumulation of the urine. The secretory action of the kidneys is 

 constant ; and the urine, passing along the ureter, accumulates in the 

 bladder, to be expelled at intervals. As now seen in its distended 

 condition, the bladder is not wholly contained within the pelvic cavity, 

 but projects a little beyond the pubic brim. When empty, however, 

 it lies entirely within the cavity, resting on the concave upper surface 

 of the pubic bones. In form the distended viscus is ovoid. The broad 

 end, which is free and directed forwards, is termed the fundus ; the 

 narrow end has the opposite direction, and becomes continuous by a 

 constricted neck with the urethra ; the sides of the bladder are related 

 to the pelvic walls ■ and the upper surface is related to the rectum, vasa 

 deferentia, and vesiculae seminales in the male, and to the vagina and 

 uterus in the female. It is maintained in position by the peritoneum, 

 which gives it only a partial covering, and by its continuity with the 

 urethra. As already noticed, the peritoneum in passing on to it forms 

 the folds called the middle and lateral ligaments of the organ. 



The Ureters (Plates 46 and 47). Each tube having crossed the 

 inlet of the pelvis, passes across its lateral wall, sustained by a narrow 

 band of peritoneum. Finally, it is reflected inwards to perforate the 

 upper wall of the bladder, a little in advance of its neck. 



Directions.— Should the subject be a mare, the dissector must now 

 turn to page 363 et seq., where the urethra and reproductive organs of 

 the female are described. 



The Urethra in the male (Plate 47). This is a long tube, extending 

 from the neck of the bladder to the free extremity of the penis. The 

 first few inches of the tube are contained within the pelvis, between the 

 rectum and the ischiatic symphysis ; for the rest of its extent it is extra- 

 pelvic, and amalgamated with the penis except at its termination, where 

 it projects as a short tube from the glans penis. The intra-pelvic 

 division of the tube is divided into the prostatic and membranous 

 portions ; the extra-pelvic division is also called the spongy portion. 

 The prostatic portion includes the first inch or two of the tube behind 

 the neck of the bladder, and it is embraced by the prostate gland. 

 The membranous portion comprises the next two or three inches, extend- 

 ing as far as the ischial arch, where, at a very acute angle, it becomes 

 continuous with the spongy portion. It is at this angle that the point 

 of a catheter is likely to be arrested. 



Muscles. The membranous part of the urethra has connected with 



