398 



DISSECTION OF THE PERINEUM. 



Fig. 132. 



from one lateral attachment to the other, and inclosing the urethra, like 

 the sphincter ani encircles the rectum. 



Action. The muscles of both sides act as a single sphincter in dimin- 

 ishing the membranous part of the urethra, and ejecting the contents of 



the tube. Like the ejaculator, they are 

 relaxed whilst the urine is passing, but 

 the two contract forcibly in expelling 

 the last of that fluid. 



Involuntary circular fibres within 

 the constrictor muscle surround the 

 urethra from the bulb to the prostate, 

 and form a layer about ^th of an inch 

 thick ; they are not fixed to bone, and 

 are continuous behind with the circular 

 fibres of the prostate. This layer is a 

 portion of the large involuntary muscle, 

 of which the prostate is chief part, 

 surrounding the beginning of the 

 urethra. 1 



Action. This involuntary layer as- 

 sists in moving forwards the urine and 

 the semen. 



The glands of Cowper will be found 

 by cutting through the transverse mus- 

 cle. They are situate below the mem- 

 branous part of the urethra, one on 

 each side of the middle line, and close 

 behind the bulb. Each gland is about 

 the size of a pea, and is made up of 

 lobules; and the lobules are composed 

 of small vesicles, which are lined by flattened epithelium. 



Connected with each is a minute duct, nearly an inch in length, which 

 perforates obliquely the wall of the urethra (corpus spongiosum), and 

 opens into the urethral canal about half an inch in front of the triangular 

 ligament. Its aperture in the ordinary state does not admit a bristle. In 

 the wall of the duct are unstriated muscular fibres ; and the interior is 

 lined by a columnar epithelium. The nature of the secretion of the gland 

 is not known. 



These bodies are sometimes so small as to escape detection, and they 

 appear to decrease in size with advancing age. 



Dissection. The student may complete the examination of the perinaeum 

 by tracing out the pudic vessels and nerve, and their remaining branches. 

 From the point of its division beneath the ci'us into two branches (dorsal 

 of the penis, and cavernous), the artery is to be followed backwards, along 

 the pubic arch of the left side. The pudic nerve will be by the side of, 

 but deeper than the artery. 



PUDIC ARTERY (a). The posterior half of this artery has been already 

 dissected (p. 390). In the anterior half of the perinamm it ascends be- 

 tween the layers of the triangular ligament, and along the pubic arch 

 nearly to the pubes ; there it perforates the superficial part of the liga- 



THE SYMPHYSIS PUBIS SEKN FROM BEHIND 

 WITH PART OF THE URINARY BLADDER 

 ANDTHE PROSTATE, AND WITH THK TUBE 

 OF THE URETHRA SURROUNDED BY THE 

 CONSTRICTOR MUSCLE (Santorini). 



a. Bladder cut open: the swelling of the 



prostate surrounds it in front. 

 6. Constrictor urethra: 



c. Part of the muscle above, and 



d. Part underneath the urethra. 



1 See a paper on the Arrangement of the Muscular Fibres of the Urethra, in vol. 

 xxxix. 1856, of the Trans, of the Med.-Chir. Society. 



