OF THE ABDOMEN. 365 



The linea alba is a tendinous raphe seen along the middle line of the abdomen, 

 extending from the ensiform cartilage to the symphysis pubis, to which it is 

 attached. It is placed between the inner borders of the Recti muscles, and is 

 formed by the blending of the aponeuroses of the Obliqui and Transversales muscles. 

 It is narrow below, corresponding to the narrow interval existing between the 

 Recti ; but broader above, as these muscles diverge from one another in their 

 ascent, becoming of considerable breadth after great distension of the abdomen from 

 pregnancy or ascites. It presents numerous apertures for the passage of vessels 

 and nerves : the largest of these is the umbilicus, which in the foetus transmits the 

 umbilical vessels, but in the adult is obliterated, the cicatrix being stronger than 

 the neighboring parts ; hence umbilical hernia occurs in the adult near the 

 umbilicus, whilst in the foetus it occurs at the umbilicus. The linea alba is in 

 relation, in front, with the integument, to which it is adherent, especially at the 

 umbilicus ; behind, it is separated from the peritoneum by the transversalis fascia ; 

 and below, by the urachus, and the bladder when that organ is distended. 



The lineae semilunares are two curved tendinous lines placed one on each side 

 of the linea alba. Each corresponds with the outer border of the Rectus muscle, 

 extends from the cartilage of the ninth rib to the pubic spine, and is formed by 

 the aponeurosis of the Internal oblique at its point of division to enclose the 

 Rectus, where it is reinforced in front by the External oblique and behind by the 

 Transversalis. 



The linese transversse are narrow transverse lines which intersect the Recti mus- 

 cles, as already mentioned; they connect the lineae semilunares with the linea alba. 



Actions. The abdominal muscles perform a threefold action : 



When the pelvis and thorax are fixed, they compress the abdominal viscera, by 

 constricting the cavity of the abdomen, in which action they are materially assisted 

 by the descent of the diaphragm. By these means the foetus is expelled from the 

 uterus, the faeces from the rectum, the urine from the bladder, and the contents of 

 the stomach in vomiting. 



If the pelvis and spine are fixed, these muscles compress the lower part of the 

 thorax, materially assisting expiration. If the pelvis alone is fixed, the thorax is 

 bent directly forward when the muscles of both sides act, or to either side when 

 those of the two sides act alternately, rotation of the trunk at the same time taking 

 place to the opposite side. 



If the thorax is fixed, these muscles, acting together, draw the pelvis upward, 

 as in climbing ; or, acting singly, they draw the pelvis upward, and bend the 

 vertebral column to one side or the other. The Recti muscles, acting from below, 

 depress the thorax, and consequently flex the vertebral column ; when acting from 

 above, they flex the pelvis upon the vertebral column. The Pyramidales are 

 tensors of the linea alba. 



The fascia transversalis is a thin aponeurotic membrane which lies between the 

 inner surface of the Transversalis muscle and the extra-peritoneal fat. It forms 

 part of the general layer of fascia which lines the interior of the abdominal and 

 pelvic cavities, and is directly continuous with the iliac and pelvic fasciae. In the 

 inguinal region the transversalis fascia is thick and dense in structure, and joined 

 by fibres from the aponeurosis of the Transversalis muscle, but it becomes thin 

 and cellular as it ascends to the Diaphragm, and blends with the fascia covering 

 this muscle. In front, it unites across the middle line with the fascia on the 

 opposite side of the body, and behind it becomes lost in the fat which covers the 

 posterior surfaces of the kidneys. Below, it has the following attachments : 

 posteriorly, it is connected to the whole length of the crest of the ilium, between 

 the attachments of the Transversalis and Iliacus muscles ; between the anterior 

 superior spine of the ilium and the femoral vessels it is connected to the posterior 

 margin of Poupart's ligament, and is there continuous with the iliac fascia. 

 Internal to the femoral vessels it is thin and attached to the os pubis and pectineal 

 line, behind the conjoined tendon, with which it is united; and, corresponding to 

 the point where the femoral vessels pass into the thigh, this fascia descends in 



