THE ABDOMINAL WALL 221 



1. The rectus muscle. 



2. The pyramidalis muscle. 



3. The terminal portions of the anterior branches of the lower six 



thoracic nerves. 



4. The inferior epigastric artery, some of its branches, and venae comites. 



5. The superior epigastric artery, some of its branches, and venae comites. 



Dissection. The front part of the sheath of rectus abdominis 

 has already been turned aside, now look for the pyramidalis ; if 

 it is present it will be found in the lower part of the sheath, in 

 front of the rectus, extending from the front of the os pubis and 

 the ligaments of the symphysis pubis to the lower part of the 

 linea alba ; clean it, then detach it from the linea alba, and turn 

 it downwards. As it is reflected secure its nerve of supply. It 

 is a twig of the last thoracic nerve which pierces the rectus and 

 enters the deep surface of the pyramidalis. After the attach- 

 ments of the pyramidalis have been displayed, raise the lateral 

 border of the rectus with the handle of the scalpel, and secure 

 the terminal parts of the anterior branches of the lower six 

 thoracic nerves as they enter the sheath after piercing the 

 posterior lamella of the aponeurosis of the internal oblique 

 muscle. Note that the nerves are associated with small branches 

 of the superior and inferior epigastric arteries which leave the 

 sheath through the openings by which the nerves enter. 



The posterior surface of the rectus muscle, unlike the anterior 

 surface, is not attached to the sheath by lineae transversae ; 

 therefore it can easily be raised from the posterior part of the 

 sheath and the nerves can be followed into the substance of the 

 muscle. When the facts mentioned have been verified, cut 

 the nerves between the points where they enter the sheath and 

 the points where they enter the muscle, and at the same time 

 cut the small arteries which lie beside the nerves ; then divide 

 the rectus abdominis about the middle of its length. Turn the 

 upper part of the divided muscle upwards and secure the superior 

 epigastric artery which descends into the sheath behind the costal 

 cartilages and then enters the muscle, and define the attachments 

 of the muscle to the xiphoid process of the sternum, and the 

 cartilages of the seventh, sixth, and fifth ribs. Throw the lower 

 part of the muscle downwards, secure the inferior epigastric 

 artery as it enters the sheath about midway between the umbilicus 

 and the pubis, then define the inferior attachments of the muscle 

 to the crest of the os pubis and the front of the symphysis pubis. 



M. Pyramidalis. The pyramidalis is a small triangular 

 muscle not always present which springs from the front of 

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

 into the linea alba. It lies anterior to the lower part of the 

 rectus. It is a tensor of the linea alba and is supplied by the 

 last thoracic nerve. 



M. Rectus Abdominis. The rectus abdominis is a broad 

 band of muscular fibres which stretches between the thorax 

 and the pubes, at the side of the linea alba. Inferiorly, 

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



