336 HEALTH AND DISEASE 



Obliquus Abdominis Externus (External Oblique Muscle of the 

 Abdomen). This is the outermost and the largest of the abdominal 

 muscles. It is broad behind and narrow in front, and gives off a wide 

 aponeurotic tendon, which passes obliquely downward and backward. 



Origin. From the outer surface of the thirteen or fourteen posterior 

 ribs and from the tendon of the latissimus dorsi. 



Insertion. Its fibres take an oblique direction downward and back- 

 ward, and give off a wide aponeurotic tendon, which becomes inserted 

 into (l) the linea alba in the centre of the belly, (2) the pubis, (3) the 

 external angle of the ilium or haunch -bone. Between the two last 

 named points of insertion the tendon forms an arch known as " Pou- 

 part's ligament". Near the pubis its fibres divide and form an ellip- 

 tical opening, the external ring for the passage of the testicle into the 

 scrotum. 



Action. To flex and arch the back and to assist in expiration. By 

 forcible compression of the abdomen it becomes an active agent in urina- 

 tion, defoacation, and parturition. 



Obliquus Abdominis Internus (Internal Oblique Muscle of the 

 Abdomen). Like the muscle last described, the internal oblique muscle 

 is flat, and comprises a thick, fan-shaped fleshy portion spreading out 

 from above forward and terminating in a broad aponeurotic tendon. It 

 is situated in the region of the flank, and its fibres proceed from behind 

 downward and forward, and in so doing cross those of the external 

 oblique muscle as they pass backwards. 



Origin. From the external angle of the ilium or haunch-bone, and 

 the contiguous fibres of Poupart's ligament. 



Insertion. Into (l) the symphisis pubis, (2) the linea alba, (3) and 

 the cartilages of the last four or five ribs. 



Action. The same as the external oblique. 



Rectus Abdominis (Straight Muscle of the Abdomen). A long, 

 somewhat wide muscle passing from the sternum or breast-bone in front to 

 the pubis behind. It is situated between the broad tendons of the internal 

 oblique and the transversalis muscles, and forms the principal part of the 

 floor of the abdomen. It is marked by a number of transverse lines 

 (lineae transversse), due to short tendinous intersections. It joins its 

 fellow in the middle line of the belly. 



Origin. From the sternum, and cartilages of the ribs from the 5th 

 to the 9th. 



Insertion. Into the anterior border of the pubis. 



Action. To flex the spine, and, by compressing the abdomen, to assist 

 in expiration, urination, defecation, and parturition. 



