THE ABDOMEN 905 



GUIDE TO THE DISSECTION OF THE ABDOMEN. 



Male Perineum. 



Before the subject is placed in the Uthotomy positon the dissectors should 

 practise passing the catheter, which should then be left in the urethra and 

 bladder. The subject having been placed in the lithotomy position, the penis 

 and scrotum are to be tied up to the end of the catheter. The first duty of 

 the dissector is to make himself familiar \vith the landmarks, boundaries, 

 and arbitrary' divisions of the perineum, and he should have before him a 

 ligamentous pelvis. He should also introduce his finger well into the rectum, 

 when he will feel through its upper wall the following structures in order 

 from without inwards: (i) the membranous part of the urethra, with the 

 catheter lying in it ; {2) the posterior or rectal surface of the prostate gland, 

 easily recognised by its firmness and resistance ; and (3) the external trigone 

 of the bladder, which is destitute of peritoneum. The rectum is then to be 

 Ughtly stuffed with tow, and the margins of the anal aperture are to be brought 

 together with a few stitches. Before removing the skin the dissector should 

 note the antero-posterior median raphe in the uro-genital division of the 

 perineum, and he should follow this raphe over the posterior and anterior 

 surfaces of the scrotum to the under surface of the penis. He should note 

 the position of the central tendinous point, which is about an inch in front 

 of the anus. He should also observe that the anus is situated posterior to 

 a Une connecting the front parts of the ischial tuberosities. A slight hollow 

 on the surface between the anu« and the tuber ischii indicates the situation 

 of the ischio-rectal fossa. 



To remove the skin the following incisions should be made : a median 

 incision, extending from the root of the scrotum to the tip of the coccyx, 

 and surrounding the anus ; a transverse incision, extending outwards from 

 the tip of the coccyx for fully 3 inches ; another transverse incision, extending 

 outwards from the central tendinous point for fully 3 inches ; and a third 

 transverse incision, extending outwards from the anterior extremity of the 

 median incision (at the root of the scrotum) for a similar distance. The 

 sphincter ani extemus is to be first displayed. An effort should be made to 

 show the corrugator cutis ani, but this is not an easy dissection. Between 

 the tip of the coccyx and the anus the dissector will meet with the hemor- 

 rhoidal or perineal branch of the fourth sacral nerve, and, in the region of the 

 anus and over the ischio-rectal fossa, will be found twigs of the inferior 

 hemorrhoidal nerve. The lower border of the gluteus maximus is next to 

 be dissected, taking care to preserve the gluteal cutaneous branches of the 

 small sciatic nerve and sciatic artery, and the perforating cutaneous branch 

 of the sacral plexus, the latter making its appearance near the coccyx. The 

 dissectors should conjointly make an effort to show the ano-coccygeal body, 

 which Ues in the middle line between the tip of the coccyx and the anal canal. 



The fat is to be removed from the ischio-rectal fossa, in doing which 

 its loose character is to be noted, as well as the fact that it fills up the 

 fossa, and also extends into the anterior and posterior diverticula con- 

 nected with it. In removing the fat the dissector should cut from the anus 

 outwards, taking care to preserve the inferior hemorrhoidal vessels and 

 nerve, which cross the fossa transversely. In removing the fat from the front 

 part of the fossa the superficial perineal artery and the two superficial perineal 

 nerves, external and internal, are to be preserved. The outer wall of the 

 fossa is to be dissected, showing the obturator fascia covering the obturator 

 intemus muscle, and containing Alcock's canal. Upon one side Alcock's 

 canal should be opened and its contents displayed, in the following order 

 from below upwards : the perineal division of the pudic nerve, vena comes, 

 internal pudic artery, vena comes, and dorsal nerve of the penis. The position 

 of the artery, its distance from the surface, and its relation to the tuber ischii 

 are to be noted. An opening is also to be made in the obturator fascia to 



