220 ABDOMEN 



more than 12.5 mm. (half an inch), the aponeurosis of the 

 transversalis is fixed to fully one inch of that line. 



Above the level of the falx inguinalis the aponeurosis 

 of the transversus is inserted into the linea alba, but in 

 passing medially to that insertion it presents two different 

 relations to the rectus muscle. Down to a point midway 

 between the umbilicus and pubes it passes behind the rectus, 

 and blends with the posterior lamella of the aponeurosis of 

 the internal oblique. Below that point it passes in front of 

 the rectus, and blends with the aponeuroses of the internal 

 oblique and external oblique. 



The two oblique muscles and the transversus are very 

 efficient protectors of the abdominal contents ; they contract 

 and become firm and hard when blows or pressure threaten 

 or impinge upon the abdominal wall. They help the other 

 muscles of the abdominal wall to maintain the intra- 

 abdominal pressure by means of which the abdominal 

 viscera are kept in position. They are muscles of expiration, 

 because when they contract they press upon the abdominal 

 viscera, tending to force them towards the thorax, so elevating 

 the diaphragm and reducing the capacity of the thorax. 

 They also play a part in defaecation, for their contraction 

 increases the intra- abdominal pressure and so helps the 

 rectum to evacuate its contents. All three muscles are 

 supplied by the anterior branches of the lower six thoracic 

 nerves, and by the anterior branch of the ilio-hypogastric nerve. 



Dissection. Turn now to the sheath of the rectus abdominis 

 and note that crossing it transversely are three linear thickenings, 

 the lincce transversce. One lies at the level of the xiphoid process 

 of the sternum, another at the level of the umbilicus, and the 

 third is midway between the other two. Occasionally a fourth 

 transverse linear thickening is present below the umbilicus. 

 Divide the sheath by a vertical incision along the middle line of 

 the muscle, then raise the medial and lateral parts of the divided 

 sheath from the surface of the muscle, reflect the medial part 

 towards its attachment to the linea alba, and the lateral part 

 towards the lateral border of the muscle. Between the lineae 

 transversae the sheath can be separated from the muscle with 

 the handle of the scalpel, but at the lineae transversae the front 

 of the sheath is blended with tendinous intersections in the 

 muscle, and the edge of the scalpel must be called into play. 

 As the flaps of the sheath are raised the anterior cutaneous 

 nerves must be preserved. 



Contents of the Sheath of the Rectus. Within the sheath 

 of the rectus are the following structures : 



