126 MUSCULAR hYSTEM. 



the bowels ; and, in that manner, assist both in the evacuation of 

 the faeces and urine, and also in the expulsion of the foetus. At 

 the same time, they will have the effect of diminishing the cavity 

 of the chest, in the longitudinal direction, by forcing the abdomi- 

 nal viscera against the diaphragm, and driving that muscle for- 

 wards into the form of a convexity ; and in the transverse as 

 well, though not in the same degree, by compressing and retract- 

 ing the ribs. But, in almost all their operations, they are con- 

 cerned with the diaphragm ; and, together with it, produce effects 

 that can only be understood by studying their separate and com.- 

 bined actions, 



OBLiQuus INTERN us ABDOMINIS. — ( lUo-abdominalis.) 



Situation. — Postero-lateral and inferior parts of the abdomen. 



Form. — Broad ; thin ; fan-shaped. 



Attachment. — Outwardly and posteriorly, to the spine of the 

 ileum, from which the fleshy fibres radiate : inwardly, at the linea 

 semilunaris, it becomes tendinous, and inseparably unites with 

 the aponeurosis of the external oblique ; along with which it is 

 continued to the linea alba. 



Relations. — Externally, with the former muscle; internally, 

 with the transversalis and rectus. 



Direction. — Radiated : the superior fasciculi being directed 

 towards the cartilages of the ribs ; the inferior, towards the linea 

 alba: both decussating those of the external oblique. 



Structure. — Fleshy, from the ileum to the linea semilunaris : 

 afterwards, to its termination, an expanded and loose-textured 

 tendon. 



Action. — These muscles will aid the former in sustaining the 

 weight of the viscera, as well as in compressing them : they will 

 have a more partial effect in the expulsion of the fseces and urine, 

 in consequence of being placed farther back than the preceding. 

 In any effect the oblique muscles may have in turning the body 

 to one side, the right internal oblique will co-operate with the 

 left external oblique, and vice versa. 



TRANSVEP.SALis ABDOMiNi s. — fLumbo-abdominalis.J 



Situation. — Inferior and lateral parts of the abdomen. 



Figure. — Broad; flat; quadrilateral: broader posteriorly than 

 anteriorly. 



Attachment. — Anteriorly, to the inner surfaces of the cartilages 

 of all the false ribs ; superiorly, to the transverse processes of the 

 lumbar vertebrcB ; posteriorly, to tiie anterior spinous process of 

 the ileum: inwardly, to the entire linea alba. 



