OF THE ABDOMEX. 365 



where its sheath is deficient, is separated from the peritoneum by the trans- 

 versalis fascia. 



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

 part of the abdomen, in front of the Kectus, 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 up- 

 wards, 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 proportionately increased in size. Occa- 

 sionally it has been found double on one side, or the muscles of the two sides 

 are of unequal size. Sometimes its length exceeds what is stated above. 



The Quadratus Lumborum (Fig. 228, p. 353) is situated in the lumbar region; 

 it 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 vertebra. The other portion of the muscle, situated 

 in front of the preceding, arises from the upper borders of the transverse pro- 

 cesses 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 aponeurosis of origin 

 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, lineaa semilunares, Iinea3 transverse ; when the dissection 

 of the 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 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 fcetus 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 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 dis- 

 tended. 



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 of the pubes, and is formed by the 

 aponeurosis of the Internal Oblique at its point of division to inclose the Rectus, 

 where it is reinforced in front and behind by the External Oblique and Trans- 

 versalis. 



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

 the Rectus muscle as already mentioned : they connect the Iinea3 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, 



