The Abdominal ]\[uscles. 



275 



>[. rectus abdominis 



j\liu. intercostales 

 interni 



Vagina 



m. recti 



abdominis 



posterior 

 leaf 



anterior 

 leaf 



M. transvcrsus. 

 abdominis 



Vagina m. recti 



abdominis 



(anterior leati 



M. obliquus internus abdominis 



M. obliquus externus abdominis 

 (cut through and reflected medianward) 



320. Transition of the tendon of the right 

 m. obliquus internus abdominis into the sheath 



of the rectus. 



(The m. ohliquus externus abdominis has been complete!}" removed above; below, it has been cut 

 through and reflected; the m. obliquus inteiTKis abdominis has been separated at its upper border from 

 the costal cartilages; theanterior leaf ofthe sheath oftherectushasbeenremovedin the upperportion.) 



M. obliqmisiuternus abdominis (see also Figs. 3 19, 331 and 332). Form: flat, quadran- 

 gidar, broad, in front considerably longer than behind. Position: on the anterior and lateral 

 surface of the abdomen, completely covered by the m. obliquus externus abdominis. Origin: 

 posterior surface of the combined leaves of the fascia lunibodorsalis (see p. 288), linea intermedia 

 of the iUac crest, lateral two thirds of the lig. inguinale. Insertion: the most posterior fibers 

 pass upward and forward to the inferior margins ofthe lOtii 12* rib. The other fibers coming 

 from the iliac crest diverge and pass medianward so that the uppermost run parallel to the 

 ends of the costal cartilages (connected with them only by loose tissue), the lowermost run 

 transversely; the fibers Irom the lig. inguinale are somewhat curved as they run downward. 

 All the muscle bundles not fastened to the ribs go over, lateralward from the m. rectus, along a 

 curved line, into a tendinous plate. This divides in its upper two thirds into two lamellae, of 

 which one passes in front of, the other behind, the m. rectus abdominis to go to the median 

 plane and there form the basis for the corresponding leaf of the vagina m. 7-ecti abdominis 

 (0. T. sheath of the rectus) (see also Fig. 322 and p. 279). In the lower third, all the fibers 

 run in front of the m. rectus abdominis (see also Fig. 323 and p. 279); the posterior leaf of 

 the rectal sheath is lacking here ; its lower margin is curved so as to be concave and is called 

 the linea semicircularis IDouglasi] (see Fig. 324). The lower margin of the muscle forms in 

 part the upper margin of the inguinal canal (see p. 281); in addition the m. cremaster goes off 

 from it (see p. 281j. Action: it draws the thorax downward, bends the spinal column forward 

 and toward the same side, rotates it toward the same side : when the thorax is fixed it elevates 

 the pelvis. Innervation: rami anteriores [nn. intercostales] ofthe nn. thoracales YUI XII 

 and the nn. iliohj-pogastricus and ilioinguinalis. 



