OF THE ABDOMEN. 287 



the situation where its sheath is deficient, is separated from the peritoneum by the 

 transversalis fascia. 



The Pyramidalis is a small muscle, triangular in form, placed at the lower 

 part of the abdomen, in front of the Rectus, and contained in the same sheath 

 with that muscle. It arises by tendinous fibres from the front of the os pubis 

 and the anterior pubic ligament ; the fleshy portion of the muscle passes upwards, 

 diminishing in size as it ascends, and terminates by a pointed extremity, which is 

 inserted into the linea alba, midway between the umbilicus and the os pubis. 

 This muscle is sometimes found wanting on one or both sides.; the lower end of 

 the Eectus then becomes proportionally increased in size. Occasionally it has 

 been found double on one side ; at times the muscles of the two sides are of unequal 

 size. Sometimes its length exeeds that stated above. 



The Quadratus Lumborum is situated in the lumbar region, is irregularly 

 quadrilateral in shape, broader below than above, and consists of two portions. 

 One portion arises by aponeurotic fibres from the ilio-lumbar ligament, and the 

 adjacent portion of the crest of the ilium for about two inches, and is inserted 

 into the lower border of the last rib, about half its length, and, by four small 

 tendons, into the apices of the transverse processes of the third, fourth, and fifth 

 lumbar vertebrae. The other portion of the muscle, situated in front of the pre- 

 ceding, arises from the upper borders of the transverse processes of the third, 

 fourth, and fifth lumbar vertebra and is inserted into the lower margin of the 

 last rib. The Quadratus lumborum is contained in a sheath formed by the anterior 

 and middle lamellae of the vertebral aponeurosis of the Transversalis. 



Nerves.' The abdominal muscles are supplied by the lower intercostal, ilio- 

 hypogastric, and ilio-inguinal nerves. The Quadratus lumborum receives filaments 

 from the anterior branches of the lumbar nerves. 



In the description of the abdominal muscles, mention has frequently been made 

 of the linea alba, lineae semilunares, lineae transversae ; when the dissection of 

 these muscles is completed, these structures should be examined. 



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

 abdomen, extending from the ensiform cartilage to the pubes. It is placed 

 between the inner borders of the Recti muscles, and formed by the blending of 

 the aponeuroses of the Oblique and Transversalis muscles. It is narrow below, 

 corresponding to the narrow interval existing between the Eecti, 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 neigh- 

 boring parts ; hence the occurrence of umbilical hernia in the adult above 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 linese 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 eighth rib to the pubes, and is formed by the 

 aponeurosis of the Internal oblique at its point of division to inclose the Rectus. 



The linese transversae are three or four narrow transverse lines which intersect 

 the Rectus muscle, as already mentioned, and connect the lineae semilunares with 

 the linea alba. 



Actions. The abdominal muscles perform a threefold action. 



1. When the pelvis and thorax are fixed, they can 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 ingesta from the stomach in vomiting. 



