vm THE EXCRETION OF URINE 461 



are composed pass from one layer to another, and are united by 

 connective tissue. It is also an artificial distinction to regard 

 the longitudinal fibres collectively as one muscle, the detrusor 

 urinae, because the layer in which the fibres are mostly circular 

 must also contribute to the compression of the vesicular cavity 

 and increase of pressure within it, and thus to the expulsion of 

 the urine. The term "musculus detrusor" should comprise the 

 entire muscular coat of the bladder, which, as a whole, constitutes 

 a hollow muscle consisting of a tissue of plain fibres. 



Anatomists are not agreed as to whether there is an internal 

 sphincter of plain muscle at the neck or urethral orifice of the 

 bladder, independent of the layer of circular fibres described 

 above, and of the external sphincter of striated muscle ( Wilson's 

 or Guthrie's muscle} which is certainly under direct voluntary 

 control. Griffiths in England (1891), and Versari in Italy (1897), 

 devoted themselves to this subject. The former denied the 

 existence, not only for man, but for mammals and vertebrates in 

 general, of an internal sphincter resicae independent of the circular 

 muscle fibres of the bladder. According to Griffiths, there is no 

 thickening of the muscular fibres near the urethral orifice to 

 justify the term " sphincter." But the question whether there 

 is or is not a sphincter in the bundle of circular fibres that 

 surrounds the neck of the bladder, ought not to depend on 

 whether this bundle is thicker than the circular layer of the 

 bladder or not, but on whether it has any special structure and 

 distinct physiological function. In regard to structure Versari's 

 researches seem to us exhaustive. He admits the existence of an 

 internal sphincter in both sexes, in adults as well as in infants 

 and children, for man as well as other mammals. According to 

 Versari there is a distinct formation shown by the peculiar 

 arrangement of the fibres, the greater compactness of the bundles 

 and their smaller size, and lastly by the smaller quantity of in- 

 terstitial connective tissue (Fig. 127). As regards specific function, 

 it is evident that while contraction of the muscular coat of the 

 bladder drives out the contents, and acts as a musculus detrusor 

 urinae, the tonic contraction of the internal sphincter prevents 

 incontinence of the bladder, i.e. escape of urine in the intervals 

 between one micturition and another. The function of the 

 sphincter is therefore diametrically opposed to that of the detrusor. 



Some authors (Wittich, Lesser, Rosenthal) have concluded 

 from the fact that urine can be retained in the bladder even in a 

 dead body, that no tonic contraction of the sphincters is required, 

 but that the simple elasticity of the tissues is enough to prevent 

 incontinence. Eetention of the urine in a dead subject, however, 

 depends on the contracture which appears in the plain muscles 

 after the death of the nerve centres, and persists until the advent 

 of rigor mortis (S. Mayer), during which the bladder of the dead 



