THE ABDOMEN, EXTERIOR. 447 



micturition, vomiting, parturition, expiration. If one acts 

 it rotates the thorax to the same side, or the pelvis to the 

 opposite side, and flexes the spine laterally. Both acting 

 will flex the thorax upon the pelvis or the reverse. 



Nerve Supply. Page 453. 



DISSECTION. 



At the level of the anterior superior spine of the ilium make a small trans- 

 verse cut through the aponeurosis of the external oblique, until the muscle 

 beneath is seen. Insert a knife-handle or finger in this opening, and, raising 

 the external oblique, divide it transversely toward the medial line, until the 

 linea semilunaris is reached. Reflect the upper part of the muscle, first raising 

 it carefully from the one beneath, and dividing its aponeurosis over the linea 

 semilunaris ; cut away the two or three upper costal attachments of the muscle 

 and turn it backward as far as it will go. The lower portion is to be turned 

 back in a similar manner, dividing the aponeurosis as near the linea alba as 

 convenient, and down to the pubis. This leaves a triangular flap attached by 

 Poupart's ligament, and showing the external ring. 



Obliquus Internus Abdominis. Fig. 89. 



Origin. From the posterior layer of the lumbar fascia, 

 from the anterior two-thirds of the middle lip of the iliac 

 crest, and from the outer half of Poupart's ligament. 



Insertion. By the conjoined tendon into the iliopectineal 

 line and crest of the pubes, by its aponeurosis into the 

 whole length of the linea alba from ensiform to symphysis, 

 and by muscular fibres into the lower borders of the last 

 three or four ribs. 



The conjoined tendon is formed by the union of the 

 fibres of the internal oblique and transversalis muscles, in- 

 ternal to the middle of Poupart's ligament, into a common 

 tendon, that is inserted into the iliopectineal line and crest 

 of the pubes. The conjoined tendon lies directly back of 

 the external abdominal ring, and strengthens this naturally 

 weak spot. The fibres of the muscles passing into the con- 



