THE ABDOMINAL WALL 231 



part of the aponeurosis of the internal oblique to form the falx 

 inguinalis, has already been examined (see p. 214). The upper 

 part enters into the formation of the sheath of the rectus abdo- 

 minis ; from the lower margin of the thorax to halfway between 

 the umbilicus and the symphysis pubis it blends with the posterior 

 lamella of the internal oblique aponeurosis, medial to the border 

 of the rectus, and it takes part, therefore, in the formation of the 

 posterior part of the sheath of the rectus. Below halfway 

 between the umbilicus and the symphysis pubis it passes in front 

 of the rectus and blends with the aponeurosis of the external 

 and internal oblique muscles to form the lower part of the 

 anterior wall of the sheath. 



In the area lateral to the sheath of the rectus abdominis the 

 only structures which now separate the dissector from the cavity 

 of the abdomen are, the transversalis fascia, the extra-peritoneal 

 fat, and the peritoneum. Do not attempt to reflect the trans- 

 versalis fascia as a whole, but make an incision through it, near 

 the margin of the ribs or near the iliac crest, to display the extra- 

 peritoneal fat, then scrape away the fat to display the peritoneum ; 

 finally, make a small incision through the peritoneum and insert 

 the finger through it into the abdomen, but do not enlarge 

 the opening, and do not disturb the contents of the abdomen. 



If the subject is a male the dissectors should now examine 

 the scrotum, and after they have gained a general idea of its 

 constituent parts they should proceed to dissect it. 



Scrotum. The scrotum is a pendulous purse-like arrange- 

 ment of the skin and superficial fascia for the lodgment of 

 the testes. The skin composing it is of a dark colour and 

 rugose, and is traversed, along the middle line, by a median 

 raphe cr ridge, which indicates its bilateral character. 



The superficial fascia possesses certain characters peculiar to 

 itself. It has a ruddy colour, and is totally devoid of fat. 

 The ruddy tint is due to the presence of involuntary muscular 

 fibres which take the place of the fat, and constitute what 

 is called the dartos muscle. The rugosity of the scrotal skin 

 is maintained by the tonic contraction of the fibres of the 

 dartos muscle. But, further, the dartos muscle forms an 

 imperfect septum or partition, which divides the interior of 

 the scrotum into two chambers one for each testis. The 

 points mentioned in connection with the construction of the 

 scrotum have all, to a certain degree, been noted in the 

 dissection of the perineum. 



The two scrotal tunics, however, are not the only coverings 

 of the testis. Each constituent of the abdominal wall has 

 been seen to contribute an investment to the spermatic cord, 

 and each in turn is continued down so as to clothe the 

 testis. Presuming, then, that the skin and superficial fascia 

 ii 15 c 



