RECTUS MUSCLE. ABDOMINAL LINES. 255 



three distinct parts of unequal size. Some fibres also are generally found 

 attached to the ensiform cartilage. 



The fibres of the rectus muscle are interrupted by three or more irregular 

 tendinous intersections, named lince. trans versce. The three which are most 

 constant are placed, one opposite the umbilicus, another on a level with the 

 ensiform cartilage, and the third intermediately between them : and these 

 generally run across the whole muscle. When one or two additional trans- 

 verse lines occur, they are usually incomplete ; one of them is very gene- 

 rally placed below the umbilicus, the position of the other is variable. The 

 intersections do not usually penetrate the whole thickness of the muscle, but 

 are confined chiefly to its anterior fibres, and are firmly united to the anterior 

 wall of the sheath of the muscle, while the posterior surface of the muscle has 

 no attachment to the sheath. 



The lineae transversse may be regarded as indications of the abdominal ribs of some 

 of the lower animals ; they sometimes extend outwards from the rectus, and penetrate 

 partially into the internal oblique. 



The pyramidalis is a small muscle resting on the lower part of the rectus. 

 It arises from the front of the pubes and the ligaments of the symphysis 

 and becoming narrow as it ascends over the lower third of the interval 

 between the umbilicus and pubes, is inserted into the linea alba. 



The pyramidalis is covered in front by the aponeurosis of the other muscles, and 

 rests posteriorly on the rectus, the size of the lower part of which is augmented when 

 the pyramidalis is wanting. 



This muscle is often absent on one or both sides : in some instances it has been 

 found to be double. It occasionally exceeds the length above stated. 



The linea alba is a white fibrous structure, extended perpendicularly 

 downwards in the middle line from the ensiform cartilage to the pubes. This 

 tendinous band is formed by the union of the aponeuroses of the two 

 oblique and the transverse muscles, the tendinous fibres being continued in 

 a decussating manner from one side to the other. Some longitudinal 

 fibres are distinguishable towards its lower end. It is broader superiorly 

 than inferiorly, and a little below the middle is widened out into a 

 circular flat space, in the centre of which is situated the cicatrix of the 

 umbilicus. 



The linece semilunares are the two curved linear spaces on the surface of 

 the abdomen, placed externally to the outer margins of the recti muscles. 

 They are produced by the absence of muscular fibres behind that part of 

 the aponeurotic tendons ; they correspond on their inner side to the outer 

 margin of the sheath of the rectus, and on their outer side mainly to the 

 line of termination of the fibres of the oblique muscles in their aponeuroses. 



The quadratus lumborum is an irregularly quadrilateral muscle, slightly 

 broader below than above, placed between the last rib and the crest of the 

 ilium, close to the vertebral column. It is divisible into two parts. One 

 of these, arising by fleshy and tendinous fibres from the ilio-lumbar ligament, 

 and from the iliac crest for several inches near the place where that ligament 

 is attached, is inserted into the inferior border of the last rib for about half 

 its length, and by four tendinous slips into the transverse processes of the 

 four superior lumbar vertebrae. Another series of fibres, arising by two or 

 three tendinous slips from as many of the inferior transverse processes at 

 their upper margins, passes in front of those inserted into the same processes, 

 and joins with the part of the muscle attached to the rib. 



