A diverticulum of the bladder is a cavity in closest relation to it produced by a localized dilatation of its wall. Diverticula are characterized by a definitely circumscribed opening which represents the connection between the cavity and the bladder, and by a mucous lining which is continuous with that of the bladder.Vesical diverticula have been classified into various groups: congenital and acquired, true and false, solitary and multiple, and traction diverticula. They have been divided into those of the dome, of the lateral walls, and of the floor of the bladder.Some authors have grouped these sacs as congenital and acquired, basing the division on the layers present. Klebs,1 Englisch2 and Rokitansky3 stated that the presence of all layers of the bladder wall designated a diverticulum of congenital origin, while in the acquired type there was merely a prolapse of the mucosa between the muscle fibers. Hinman 4 states that the classification of Englisch and Rathbun5 into true and false diverticula cannot be made, and he believes that they are all acquired. Kneise°s ays that the overwhelming majority are surely not of congenital origin, and that at most the anläge for their formation is present in embryonic life. He stresses the fact that the weakness in the muscularis is a site of predilection for the forma¬ tion of diverticula. Thomas states that at least 80 per cent are acquired through some obstructive process. Opposing this opinion, Lower considers most of them congenital.Embryologie studies by Keibel,7 Reichel8 and Ret¬ terer 9 afford at the most only suggestive hypotheses. The experimental work of Rose showed that diverticula are congenital to the extent that a loose fibrous pathway must be present through the bladder wall before the acquired factor, namely, a raised intracystic pressure, can herniate the mucosa. Lowsley and Gutierrez10 state that "it would seem, therefore, that there is a possibility that vesical diverticula are primarily con¬ genital, although there is a greater likelihood of their manifestation during late adult life, which may be due to the occurrence of factors inducing abnormal tension within the bladder."Herbst and his collaborators, as a result of numerous experiments on dogs, state that "increased intracystic pressure during micturition such as may be produced by spasmodic contractions of the detrusor muscle due From the Michael Reese Hospital and the Edward Hines, Jr., Hospital.1. Klebs, cited by Englisch (footnote 2).