222 ABDOMEN 



attached to the pubic crest, whilst the medial and smaller 

 is fixed to the ligaments in front of the symphysis pubis. 

 Towards the thorax the muscle widens and becomes thinner, 

 and its insertion is effected by three large slips into the anterior 

 aspect of the costal cartilages of the fifth, sixth, and seventh 

 ribs, and by a smaller slip to the xiphoid process of the 

 sternum. 



The rectus muscle is broken up into segments by irregular 

 tendinous intersections the inscriptions tendinecz or linece, trans- 

 verse. They are usually three in number, and are placed, 

 one at the level of the umbilicus, another opposite the xiphoid 

 process, and a third midway between. A fourth intersection 

 is sometimes found below the level of the umbilicus. The 

 tendinous intersections are adherent to the anterior part of the 

 sheath of the rectus ; but they have no attachment to the 

 posterior part of the sheath. 



The rectus abdominis protects the abdominal contents. 

 It becomes firm and hard when pressure on the front of the 

 abdominal wall threatens or occurs, and by its tonicity it 

 helps to maintain the intra-abdominal pressure. It depresses 

 the ribs to which it is attached and presses upon the 

 abdominal contents. It is, therefore, a muscle of expiration 

 and defaecation, and, as it pulls the front of the thorax 

 downwards towards the symphysis, it is a flexor of the 

 vertebral column. It is supplied by the anterior branches 

 of the lower six thoracic nerves. 



Vagina Eecti Abdominis (Sheath of the Rectus). The 

 dissector is now in a position to study the manner in which the 

 sheath of the rectus is formed. An examination of the relations 

 which the aponeuroses of the three flat muscles of the abdomen 

 bear to the rectus will show that the sheath is incomplete, 

 and does not entirely surround the rectus. It is deficient 

 posteriorly, both above and below. 



From the lower margin of the thorax to a point midway 

 between the umbilicus and pubes it encloses the rectus upon 

 all sides. In that part of its extent the anterior wall is formed 

 by the aponeurosis of the external oblique fused with the anterior 

 layer of the aponeurosis of the internal oblique, whilst the 

 posterior wall is formed by the posterior layer of the apo- 

 neurosis of the internal oblique fused with the aponeurosis of 

 the transversus abdominis (Fig. 98). 



Superiorly, the rectus muscle rests directly upon the costal 



