398 ABDOMEN 



rectus. After supplying it with twigs, they come forward from 

 its substance as the anterior cutaneous nerves of the abdomen. 



M. Rectus Abdominis (Rectus Muscle). This is a broad 

 band of muscular fibres which stretches between the thorax 

 and the pubes, on each side of the linea alba. Inferiorly 

 it arises by two heads ; of these, the lateral and larger is 

 attached to the pubic crest, whilst the medial and smaller 

 is fixed to the ligaments in front of the symphysis pubis 

 (Fig. 74, p. 200). 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. 



The rectus muscle is broken up into portions by irregular 

 tendinous intersections the inscriptiones tendinecc or lima trans- 

 verse. These 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 umbilicus. These tendinous 

 intersections are closely adherent to the sheath of the rectus 

 in front, they have no attachment to the sheath behind, a fact 

 which can be demonstrated by raising the muscle. 



M. Pyramidalis. This is a small triangular muscle 

 not always present which springs from the front of the pubes 

 and the ligaments of the symphysis, and is inserted into the 

 linea alba. It lies anterior to the lower part of the rectus, and 

 is supposed to act as a tensor of the linea alba. 



The nerve of supply to the pyramidalis comes from the last thoracic nerve. 

 To bring it into view the muscle must be carefully detached from the linea 

 alba and turned downwards towards the pubes. The nerve will be exposed 

 entering its deep surface. 



Vagina Recti 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, in 

 so far as the rectus is concerned. 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. Here the anterior wall or lamella is formed by the 

 aponeurosis of the external oblique fused with the anterior 

 layer of the aponeurosis of the internal oblique, whilst the 



