THE ABDOMEN, EXTERIOR. 453 



of the appendix vermiformis, or for the formation of an 

 artificial anus in either iliac fossa, the criss-cross arrange- 

 ment of the fibres forming a reliable sphincter in the latter 

 case. 



DISSECTION. 



Incise the sheath of the rectus muscle from the ensiform to the symphysis, 

 three-fourths of an inch from the linea alba. Reflect the two portions, 

 being careful to avoid cutting into the muscle at the tendinous intersections, 

 which are attached to the anterior portion of the sheath, but not to the 

 posterior. 



The Pyramidalis. Fig. 91. 



This small triangular muscle is found lying upon the 

 rectus at its lower part. 



Origin, From the crest, anterior surface of body and 

 symphysis of the pubes. 



Insertion. By a slender tendon into the linea alba, half- 

 way between the umbilicus and symphysis. 



Action. To make the linea alba taut, to assist the 

 rectus. 



Rectus Abdominis. Fig. 91. 



Origin. By a direct tendon from the crest of the pubes, 

 by a reflected tendon from the structures in front of the 

 symphysis across the middle line. 



Insertion. Into the front of the cartilages of the fifth, 

 sixth and seventh ribs, and outer margin of the ensiform. 



Action. To compress the viscera and aid in all expul- 

 sive efforts, as defalcation, micturition, vomiting, expira- 

 tion, parturition. To flex the spine anteriorly, bringing 

 the thorax and pelvis nearer together. 



Nerve Supply for all the Abdominal Muscles. The six 

 lower intercostal nerves and the iliohypogastric and ilio- 

 inguinal branches of the first lumbar nerve. 



