250 



DISSECTION OF THE PERINEUM. 



Transverse 

 ligament. 



Deep 



transverse 

 muscle. 



Use of 

 constrictor. 



Circular 

 fibres of 

 urethra, 



from the 

 prostate to 

 the bulb : 



Cowper's 

 glands : 



situation, 

 size, and 

 structure ; 



length and 

 termination 

 of the duct 



they vary 

 in size. 



Dissection 

 of vessels 

 and nerve. 



Piidie 

 artery : 



course and 

 ending. 



urethra, where they are interrupted in some cases by a small median^ 

 tendon. At the anterior border of the muscle there is a short fibrous ; 

 band stretching across between the inferior rami of the pubic bones, 

 and bounding, with the sub-pubic ligament at the lower margin of the! 

 symphysis, an oval opening, through which the dorsal vein of the<i 

 penis enters the pelvis. The hindmost fibres of the constrictor are-! 

 connected with the central point of the perineum, and are sometimes 

 described separately as the transversus perinei profundus. 



Action. This muscle acts as a sphincter in narrowing the 

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

 tube. It may also aid in producing erection of the penis by com- 

 pressing the veins of the corpora cavernosa, which are surrounded by 

 its fibres. 



Involuntary circular fibres within the constrictor muscle surround 

 the urethra from the bulb to the prostate, and form a layer about 

 ith of an inch thick ; they are not fixed to bone, and are con- 

 tinuous above with the circular fibres of the prostate. This layer is 

 a portion of the large involuntary muscle, of which the prostate 

 contains the chief part, surrounding the beginning of the urethra. 



Action. This involuntary layer assists in forcing forwards the 

 urine and the semen. 



THE GLANDS OF COWPER will be found by cutting through some 

 of the hinder fibres of the constrictor muscle. They are situate 

 behind the membranous part of the urethra, one on each side of the 

 middle line, and close above the bulb. Each gland is about the size 

 of a pea, and is made up of small lobules. They are hard to the feel 

 and can often be located by grasping a portion of the surrounding 

 muscle in the forceps before its removal. 



Connected with each is a minute duct, an inch or more in length, 

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

 and opens into the canal about three-quarters of an inch in front of 

 the triangular ligament. Its aperture in the ordinary state does not 

 admit a bristle. 



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

 they appear to decrease in size with advancing age. 



Dissection. The student should now trace out on the right side 

 the pudic vessels with their remaining branches, and the dorsal nerve 

 of the penis. From the point of its division beneath the cms into 

 two branches (dorsal of the penis, and cavernous), the artery is to be 

 followed backwards along the bone ; and the nerve will be found by 

 the side of, but deeper than the artery. 



The INTERNAL PDDic ARTERY has already been dissected in the 

 posterior half of the perineum (p. 242). At the front of the ischio- 

 rectal fossa it penetrates the base of the triangular ligament, and then 

 runs forwards close to the edge of the hip-bone (fig. 94, a), in a canal 

 formed by the tendinous origin of the constrictor urethrce. About 

 half an inch behind the symphysis pubis it pierces the inferior layer 

 of the ligament, and immediately divides into the arteries of the 

 corpus cavernosum and the dorsum of the penis. It is accompanied by 



