Dictionary.net

This abscess is so called from the matter being found on the side of the psoas muscle, or betwixt that and the iliacus internus. Between these muscles is a quantity of loose, areolar substance; and when an abscess takes place there, it can find no outlet except by a distant course. Generally, it descends along the psoas muscle, forming a swelling immediately beneath Poupart's ligament; at times, however, it extends down the thigh under the fascia. Severe hectic follows the bursting of the abscess, and often death. Its causes are, - scrofula, injury to the loins, etc. When, from the pain of the back continuing for some time, with other symptoms, the disease is suspected, caustics, or the moxa, applied opposite the transverse processes of the lumbar vertebrae, may be recommended; and, when the abscess is ready for opening, it may be emptied by repeated discharges of the matter, through a small opening, made with a lancet, or small, lancet-pointed trocar. The medical treatment consists in supporting the system, under the great restorative efforts required of it.