PRACTICAL CONSIDERATIONS : THE ABDOMEN. 531 



that they are diverted into the psoas sheath between those slips of origin of the 

 muscle which come from the bodies of the vertebrae and those which come from 

 the transverse processes. Often the pus descends, as in iliac abscess, to point on 

 the thigh external to the femoral vessels, but not infrequently it passes under the 

 external arcuate ligament or penetrates the psoas sheath at its outer edge and 

 the anterior layer of the lumbar aponeurosis (to which it is there attached) apd 

 points in the loin, in which case it may be mistaken for one of the abscesses origi- 

 nating in or spreading through the subserous areolar tissue. 



In the typical psoas abscess the thigh is flexed to relax the muscle and its 

 sheath and to lessen the compression of the lumbar nerves which are contained 

 within it. It will be observed that a psoas or a true iliac abscess is in close relation 

 to these nerves, but is separated from the iliac vessels and, except at the upper por- 

 tion, from the genito-crural nerve by the thick iliac fascia. Iliac aneurism may, 

 however, by pressure cause flexion of the thigh and pain in the course of the same 

 nerves. 



LANDMARKS AND TOPOGRAPHY OF THE ABDOMEN. 



1. The bony and cartilaginous sb-iutures that constitute the apparent limits of 

 the abdomen, and that are either visible or palpable, are as follows : 



(^a) The tip of the ensiform cartilage, on a level with the lower part of 

 the body of the tenth dorsal vertebra, {^b) The seventh, eighth, ninth, and teyith 

 costal cartilages, forming the lateral boundaries of the infrasternal fossa (Fig. 173, 

 page 171). A notch that may be felt on the costal border indicates the point of 

 union of the tip of the tenth to the edge of the ninth cartilage (Woolsey). (r) The 

 tips of the eleveiith and tzvelfth costal cartilages are free, except as they are con- 

 nected with each other by the intercostal and abdominal muscles. Sometimes the 

 twelfth rib is rudimentary and does not project beyond the external edge of the 

 erector spinae muscle. Hence in planning operations that open the abdominal cavity 

 just below that rib — as in nephrotomy — it is well to count the ribs from above ; other- 

 wise the pleura might be opened by mistake (Fig. 1581). ( ^) The spines of the 

 lumbar vertebrce, corresponding to their bodies and representing the posterior bony 

 wall of the abdomen, are useful landmarks. Their relation to the abdominal con- 

 tents as to level has been described (page 148). (<?) The crest of the iliicrti, the 

 anterior and posterior iliac spines, and the pubic spine and symphysis have been 

 described (page 349). 



2. The skin is usually creased or furrowed in proportion to the amount of 

 subcutaneous fat or — in thin persons — to the muscular development. In fat per- 

 sons two deep tra7isverse firrozvs form across the abdomen. In the upper one, 

 which intersects the umbilicus, the latter may be completely concealed. The lower 

 one runs just above the crest of the pubes. Its point of intersection with the 

 linea alba is a convenient landmark for the introduction of the trocar in suprapubic 

 tapping of a distended bladder. It is of use in the diagnosis of femoral hernia 

 (page 1774). 



In cases of ankylosis of the hip-joint transverse creases may be seen running 

 across the belly between the umbilicus and the pubes. They are produced by the 

 freer bending of the spine that is apt to occur in such cases, the absence of some of 

 the simpler movements of the hip-joint in flexion and extension being compensated 

 for by increased motion of the vertebral column (Treves). 



The stricz gravidarum are sinuous, silvery streaks, resembling scars, that follow 

 atrophy of the connective-tissue layers of the skin from stretching due to abdom- 

 inal distention, as in pregnancy, ovarian cysts, or ascites. 



3. Intermuscular or Interfascial Markings. — The liiiea alba — the fibrous raphe 

 formed by the union of the sheaths of the recti at their inner borders — may be seen 

 as a very shallow groove extending from the ensiform cartilage to the umbilicus. 

 Below the tip of the xiphoid this may be a quarter of an inch in breadth, and it 

 is apt to be slightly wider just above the umbilicus. From a little below that level 

 — one to two inches — it cannot be seen, as until it nears the symphysis it is merely 

 a line of fibrous tissue resulting from the coalescence of the sheaths. A little 



