394 



APPLIED ANATOMY. 



Petit's Triangle (trigonum lumbale). Above the middle of the crest of 

 the ilium is a small triangular space formed by the edge of the external oblique in 

 front, of the latissimus dorsi behind, and the crest of the ilium below. Its floor is 

 formed by the internal oblique muscle, and it is called the triangle of Petit. It forms 

 a weak point in this region through which collections of pus or, more rarely, ventral 

 herniae, may make their appearance (Fig. 407) . 



Fascial Triangle. .Above and a little posterior to Petit's triangle is another 

 triangular space. Its base is the twelfth rib, its anterior side is the posterior edge 

 of the internal oblique, and posterior side is the outer edge of the quadratus ium- 

 borum. It is also called the triangle of Grynfelt and Lesshaft. The lower portion 

 of the kidney lies immediately beneath it and the latissimus dorsi covers it (Figs. 

 408 and 409). 



Serratus posticus inferior 



Latissimus dorsi 



Eleventh rib 

 Iliohypogastric nerve 

 Ilio-inguinal nerve 



Fascial triangle and 

 kidney beneath 



Internal oblique 

 Iliohypogastric nerve 



FIG. 408. The lumbar region; the latissimus dorsi has been turned back and the external oblique cut away, reveal- 

 ing the fascial triangle. 



Lumbar Abscess. Pus in the lumbar region usually originates from caries of 

 the vertebrae, from calculus or other renal or perirenal affections, or, if on the right 

 side, sometimes from disease of the appendix. Empyemas may likewise point in this 

 region. Pus starting from the vertebrae may push its way outward under the 

 transversalis aponeurosis (anterior layer of the lumbar fascia) and perforate the trans- 

 versalis muscle where the iliohypogastric, ilio-inguinal, and last thoracic nerves enter 

 and thus reach the -under surface of the internal oblique and perforate this muscle to 

 find its exit at Petit's triangle. Pus may also perforate the floor of the fascial 

 triangle and follow the anterior surface of the latissimus dorsi down until it points in 

 the angle between the posterior portion of the crest of the ilium and the spine. The 

 quadratus lumborum muscle is thin, and its outer edge, which is not covered by 

 the erector spinae muscle, is readily pierced by pus. The erector spincz is a thick 

 muscle covered both anteriorly and posteriorly by the thick middle and posterior 

 layers of the lumbar fascia, hence pus does not pierce it but always goes around its 

 outer side. . 



Lumbar hernia usually results from the giving way of a scar from an operation. 



