254 THE ABDOMEN AND PELVIS 



long, and extends downwards,, forwards, and medially to the 

 Subcutaneous Inguinal (Ext. Abd.) Ring, where the spermatic 

 cord emerges from the abdominal wall. The subcutaneous 

 inguinal ring is a triangular opening situated in the external 

 oblique aponeurosis. Its base is formed by the lateral part 

 of the pubic crest, and its apex is directed upwards and laterally. 

 The upper (or medial) and lower (or lateral) margins of the 

 opening, known as the Crura or Pillars., are formed by the 

 external oblique aponeurosis. 



The upper or deep end of the canal is therefore placed 

 lateral to the lower or superficial end. This arrangement 

 greatly diminishes the weakness produced in the anterior 

 abdominal wall by the passage through it of the spermatic cord, 

 for when the viscera are pressed against the abdominal inguinal 

 (int. abd.) ring, e.g. in coughing, they are at the same time 

 pressed against the posterior wall of the canal, which they force 

 into apposition with its anterior wall. In this way the canal is 

 practically closed. 



The Anterior Wall of the inguinal canal is formed by the 

 aponeurosis of the external oblique ; in addition, those fibres of 

 the internal oblique which arise from the middle of the inguinal 

 ligament assist in its formation in the lateral third of the canal. 



In order to expose the spermatic cord as it lies in the inguinal 

 canal, it is necessary to cut through the external oblique 

 aponeurosis from the lower crus (pillar) of the subcutaneous 

 inguinal ring for ij inches, parallel to the inguinal ligament. 

 Medially, this incision exposes the cord, but laterally the cord 

 is still covered by the lowest fibres of the internal oblique, and 

 when they are divided the canal is laid open in its whole length. 



The Posterior Wall of the inguinal canal is formed by the 

 fascia transversalis ; medially, however, it is strengthened by 

 the falx inguinalis (conjoined tendon), which lies in front of the 

 transversalis fascia, but behind the cord (Fig. 77). 



The lowest fibres of the transversus abdominis lie above the 

 level of the lateral part of the canal, and in consequence its 

 fleshy fibres take no part in the formation of the posterior wall. 

 Its place is taken by the fascia transversalis, which descends 

 beyond the lower border of the muscle to reach the inguinal 

 ligament. The lower fibres of the internal oblique are placed, 

 at their origin, in front of the spermatic cord, but as they pass 

 medially they arch over it forming the Roof of the canal and 

 then descend behind it in the falx inguinalis (conjoined tendon). 



