THE ABDOMINAL WALL 217 



to the transversus abdominis. Minute arteries accompany 

 the nerves. 



The anterior branch of the last thoracic nerve also supplies 

 the oblique and transverse muscles, and, in addition, it gives 

 a branch to the pyramidalis muscle. 



The lateral branches of the lower thoracic nerves have 

 already been exposed and studied (p. 204). 



The ilio-hypogastric and ilio-inguinal are the lowest two 

 nerves of the series. They are directed forwards between 

 the internal oblique and the transversus, close to the crest of 

 the ilium. 



The ilio-hypogastric is the higher of the two. It gives 

 off an iliac or lateral cutaneous branch, which pierces the two 

 oblique muscles, and then crosses the crest of the ilium to 

 reach the skin of the gluteal region. The anterior portion 

 of the nerve perforates the internal oblique, a short distance 

 in front of the anterior superior spine of the ilium, and 

 then runs forwards towards the linea alba. It does not enter 

 the sheath of the rectus, but becomes superficial by piercing 

 the aponeurosis of the external oblique above the subcutaneous 

 inguinal ring. 



The ilio-inguinal nerve gives off no lateral branch. It 

 pierces the internal 'oblique, to which it gives branches, a 

 short distance above the inguinal ligament, and it becomes 

 superficial by passing through the subcutaneous inguinal 

 ring. 



M. Transversus Abdominis. The transversus abdominis 

 muscle is the deepest of the three muscular strata which enter 

 into the formation of the wall of the abdomen. It has a 

 threefold origin, viz. from the pelvis, from the vertebral 

 column, and from the costal cartilages. By its pelvic origin 

 it is attached to the lateral third of the inguinal ligament and 

 to the anterior two-thirds of the internal lip of the crest of the 

 ilium; by its costal origin it arises from the inner surfaces of 

 the costal cartilages of the lower six ribs, by a series of slips 

 or digitations which interdigitate with the slips of origin of 

 the daphragm ; by its vertebral origin it is attached, through 

 the medium of the lumbo - dorsal fascia, to the spinous 

 processes, and the tips and roots of the transverse processes, 

 of the lumbar vertebrae (Fig. 98). Indeed, the lumbo-dorsal 

 fascia constitutes the posterior aponeurosis of the muscle. 

 The manner in which the lumbo-dorsal fascia is attached to the 



