38 
DE. PETTIGEEW ON THE MUSCULAE AEEAN GEMENTS 
when the urine is actually passing through it, being perfectly closed. This is interest- 
ing, as it shows how an orifice patent only at long intervals assimilates itself to one, viz. 
the urachus, closed at birth. The closure of the urethra is favoured by the contraction 
of the very oblique or circular fibres forming the sphincter, and by the prominence of 
the uvula vesicse (luette vesicale) and median ridge in the female and the caput gallina- 
ginis or verumontanum in the male. The longitudinal, slightly oblique, oblique and 
very oblique external and internal fibres are continued into the prostatic portion of the 
urethra, so that the urethra is to be regarded as the proper continuation of the bladder 
in an antero-posterior direction. It ought, however, to be mentioned that the four outer 
layers of the bladder split up or bifurcate at the cervix, the one half going to the exter- 
nal or outer half of the urethra, the other to the prostate. There is consequently no 
portion of the bladder, urethra, or prostate in which longitudinal, slightly oblique, 
oblique, and very oblique or circular fibres may not be found. 
The longitudinal fibres of the prostate and urethra are separated by a considerable 
interval, and the very oblique or circular fibres, which are widely distinct and have 
separate axes at the cervix where the sphincter is most fully developed, curve into and 
are blended with each other in the region of the verumontanum. This is important, as it 
shows how the sphincter may act independently of the prostate, and the reverse. 
The very oblique or circular fibres have been specially described from the fact of their 
entering largely into the formation of the bladder, urethra, and prostate, and because 
they are principally concerned in the formation of the sphincter. 
The sphincter vesicee, the existence of which has been doubted, is composed of an 
anterior and posterior set of oblique and very oblique or circular fibres which is largely 
developed, and by a right and left lateral set which is accessory and less fully developed. 
The fibres of the sphincter are continuous with the oblique and very oblique spiral 
fibres of the urethra and bladder generally, and this circumstance, more than any other, 
has induced anatomists to deny its presence. As well, however, might we argue against 
the existence of a sphincter in the stomach or rectum, for in both of those cases, as is 
well known, there is continuity of structure. The fibres of the trigone are similarly 
arranged to the other internal fibres at the fundus, the very oblique or circular ones 
passing across between the uretral orifices to blend with the fibres of the ureters them-, 
selves, while the olique, slightly oblique, and vertical pass in a downward direction 
and converge prior to reaching the verumontanum, where they cross, and for the most 
part terminate. The verumontanum is thus directly connected with the fibres of the 
trigone, and indirectly with the internal fibres of the cervix generally. During the 
distended or passive condition of the bladder it acts in a downward direction as a 
mechanical wedge, and with the aid of the sphincter completely occludes the pas- 
sage of the urethra. In the active state, or when the urine is being expelled, the 
verumontanum is elevated or withdrawn by the contraction of the more vertical fibres of 
the trigone, the other vertical fibres of the fundus acting in harmony and elevating, and 
in this manner opening up, dilating, or expanding the funnel-shaped cavity within the 
