456 THE MUSCLES AND FASCIAE 



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 lineae transversae are three narrow transverse lines which intersect the 

 Recti muscles, 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 rotate 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 peritoneum. 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. Below, it has the following attachments : external 

 to 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 front of them, forming the anterior 

 wall of the crural sheath. The spermatic cord in the male and the round ligamerft 

 in the female pass through this fascia : the point where they pass through is called 

 the internal abdominal ring. This opening is not visible externally, owing to a 

 prolongation of the transversalis fascia on the structures, forming the infundib- 

 uliform process. 



The internal or deep abdominal ring is situated in the transversalis fascia, 



