FEMALE PERINEUM 197 



where it is surrounded by the sphincter muscle of the mem- 

 branous urethra. It leaves the deep pouch by piercing the 

 inferior fascia of the urogenital diaphragm, and at once opens 

 into the anterior part of the vestibule. Through the whole of 

 its extent it is closely attached to the anterior wall of the vagina. 



The dissector should pass a staff through the urethra and 

 trace its course to the bladder by means of the left index 

 finger introduced into the vagina. 



After the position of the urethra has been defined, place a 

 pad of tow soaked in preservative solution in the perineum 

 and stitch the skin flaps over it. On the fourth day after 

 the body has been brought into the dissecting room, it is 

 placed upon its back, and the dissectors of the abdomen 

 commence work on the abdominal wall. 



THE ABDOMINAL WALL. 



After the dissection of the perineum is completed, the 

 body is placed upon its back, with blocks under the thorax 

 and pelvis, and the dissectors of the abdomen begin the dissec- 

 tion of the abdominal wall (Fig. 91). 



External Anatomy. It is well, however, before proceeding 

 to the actual dissection, that some attention should be paid to 

 the general configuration and bony prominences of the region. 

 If the subject is obese the abdomen presents a smooth, 

 rounded, and protuberant appearance ; if, on the other hand, 

 it is spare, the abdominal wall is depressed, and the lower 

 margin of the thorax above, and the pubes, the iliac crests, 

 and the inguinal ligaments below, stand out in marked relief. 

 In the median plane the student will notice a linear depres- 

 sion extending downwards, from the lower end of the sternum, 

 towards the symphysis. The depression corresponds with the 

 position of the linea alba^ which lies, in the median plane, 

 between the two recti muscles. 



The linea alba is important to the surgeon, because it is a 

 fibrous portion of the abdominal wall and it is practically 

 devoid of blood-vessels ; consequently it is chosen as the 

 region through which the trocar is introduced into the ab- 

 domen in the operation of paracentesis abdominis or tapping. 



In the linear depression, rather nearer the pubis than 

 the xiphoid process of the sternum, is the umbilicus or navel. 

 It is a depressed and puckered cicatrix, but its floor is 



