MUSCULAR SYSTEM. 127 



Relations. — On the outer side, with the internal obhque and 

 straight muscles : on the inner side, with the faschia transversalis 

 and peritoneum. 



Direction. — Transverse, directly across the abdomen. 



Structure. — Partly fleshy ; partly tendinous : the two sub- 

 stances divided by the semilunar line, which leaves the tendinous 

 part broad, posteriorly ; the fleshy, anteriorly. 



Action. — These muscles will assist the oblique in supporting 

 the burden of the viscera, and are more advantageouly placed 

 to effectually compress them : they are consequently doing more 

 in the ultimate evacuation of the bowels. 



RECTUS ABDOMINIS. — (Sterno-pubiaUs.) 



Situation. — Infero-median part of the abdomen. 



Form. — Elongated ; flattened from above downwards : broader 

 in the middle than at either extremity. 



Attachment. — Anteriorly, to the cartilages of the six or seven 

 posterior true ribs ; and to the sternum : posteriorly to the pubes, 

 near its symphysis. 



Relations. — Anteriorly, it is placed between the pectoralis ma- 

 jor and the cartilages of the ribs ; externally, it has the united 

 tendons of the external and internal oblique; internally, that of the 

 transversalis : also, the internal pectoral and epigastric arteries; 

 and the faschia transversalis and peritoneum. 



Structure. — Tendinous at its attachments : the anterior one is 

 aponeurotic. The intermediate length is fleshy, but divided into 

 portions by about a dozen transverse tendinous interlacements or 

 intersections. Each muscle, by itself, is inclosed within a sheath, 

 formed of the united tendons of the external and internal oblique 

 muscles, inferiorly ; and of that of the transverse muscle, supe- 

 riorly. At the places where the tendinous bands exist, the sheath 

 contracts firm adhesion to the muscle; and it is this union and 

 structure that gives rise to the existence of the linea transversalis. 

 The recti occupy about one-third of the abdominal superficies. 



Action. — Their principal use appears to be that of bracing the 

 middle parts of the belly ; and, thereby, counteracting that tenden- 

 cy to relaxation which must exist from the constant dependence of 

 the bowels. They can have but little effect in compressing the 

 bowels ; though they will take some part in contracting the cavity 

 of the thorax, by drawing the sternum upwards and backwards. 



Remark. — A careful incision through some of the posterior 

 fibres of the transversalis will disclose to view an expansion of 

 faschia of considerable density and firmness of texture, which 

 corresponds to a part in the human subject first described by Sir 

 A. Cooper, and by him named the faschia transversalis. It may 



