Chap. XVI.] PSOAS ABSCESS. 319 



Retro-peritoneal abscesses in the pelvis (pelvic cellu- 

 litis) may mount up into the iliac fossae, may appear 

 as "iliac abscesses," and may ultimately discharge 

 themselves by many openings in the lower parts of 

 the anterior abdominal wall. 



It may be well to note that the common and 

 external iliac vessels, the lymphatics and the ureters, 

 are outside the iliac fascia, and rest upon its abdo- 

 minal surface, while the anterior crural nerves and 

 abdominal parts of the lumbar nerves are within 

 the osseo-aponeurotic space. Thus, the suprafascial 

 abscess may, with little difficulty, reach the thigh by 

 following the iliac vessels ; while the subfascial 

 collection would pursue the anterior crural nerve. 



A psoas abscess, or abscess within the fascial 

 sheath of the psoas muscle, is usually due to spinal 

 caries, although it may appear independently of that 

 disease. If the lumbar spine be involved, the matter 

 can pass directly into the substance of the muscle, 

 which it will more or less entirely destroy. If the mis- 

 chief be in the dorsal spine, the matter gravitates along 

 the front of the column until it reaches the diaphragm, 

 which it pierces by an inflammatory process. It is 

 now brought into relation with the heads of the psoas, 

 and has to pass through a narrow strait. "It is 

 prevented from enlarging on the fore-part by the liga- 

 menta arcuata, and at the back by the spine and lowest 

 rib ; hence, in order to proceed it has to force its way 

 in the line of the psoas muscle. That, however, can 

 only be done by peneti'ating into its interior. It ac- 

 complishes this, in the first place, by inserting its most 

 advanced part, like a wedge, between the two origins 

 (viz. from the bodies of the vertebrae, and from the 

 corresponding transverse processes) : it then splits and 

 distends the fibres, so as to form a cavity for the 

 reception of the pus .... and the psoas at length is 

 converted more or less thoroughly into an abscess" 



