272 



THE ABDOMEN AND PELVIS 



the fascial envelope while the great nerves lie external to it 



(P- 355)- 



Psoas Abscess. A cold abscess resulting from tuberculous 

 periostitis or osteo-myelitis of the lower thoracic or upper 

 lumbar vertebrae is limited in front by the anterior longitudinal 

 ligament and spreads in a lateral direction. In the lumbar 

 region it passes either into the substance of the psoas major 

 or between the muscle and its covering fascia ; in the thoracic 



Left infra-colic compartment 

 Supra-colic compartment 



Left para-colic gutter 



Vermiform process, 

 perforated 



Descending colon 



Psoas abscess 



FlG. 83. Diagram of a Transverse Section through the Abdomen, 



below the Lower Poles of the Kidneys. 



On the left side, a psoas abscess is depicted, spreading laterally behind the 

 fascial envelope of the abdomen. The pus is separated from the quadrat us 

 lumborum by the anterior layer of the lumbo- dorsal fascia, and from the 

 descending colon by the transversalis fascia. 



On the right side, an abscess is depicted in connection with a retro-caecal, 

 extra-peritoneal vermiform process. In this case the pus is situated inside 

 the fascial envelope of the abdomen. 



region it enters the posterior mediastinum and, gravitating 

 downwards, passes into the abdomen behind the medial lumbo- 

 costal arch (int. arcuate ligament), which is simply the thickened 

 upper border of the psoas fascia. In both instances, therefore, 

 the abscess lies behind the psoas fascia, and its presence may 

 excite reflex contraction of the muscle with flexion at the 

 hip-joint. A similar reflex is often observed in appendicular 

 inflammation, and in other cases where the muscle is irritated. 

 Direction of Spread. (i) The pus may pass laterally behind 



