22 
DR. PETTIGREW ON THE MUSCULAR ARRANGEMENTS 
unequal thickness, the thickest portion corresponding to the cervix in the neighbour- 
hood of the sphincter, the second thickest portion to the- apex in the vicinity of the 
urachus, the third to the trigone, the fourth and fifth to the anterior and posterior 
walls, and the sixth and seventh to the right and left lateral walls *. The most external 
and most internal loops are confined principally to one or other of the aspects indicated ; 
but the deeper or more central loops radiate and expand towards the apex and base, so 
that they come to embrace the entire circumference of the bladder in these directions. 
The expansion referred to is greatest towards the apex, and the aggregation of the 
terminal loops of the anterior and posterior fibres at the cervix (assisted by the lateral 
ones) form a well-marked sphincter in this situation. The sphincter is bilaterally 
symmetrical and oval in shape, the long axis being directed transversely, or from side 
to side, as represented at mm!, yy' of fig. 11, Plate III., and ly of diagrams 10 & 20, 
Plate V. The two sets of lateral fibres (Plate V. diagram 10, z r, vs) which assist 
in the formation of the sphincter, intersect the angles formed by the crossing of the 
anterior and posterior fibres, and render its aperture somewhat circular in appearance. 
This circumstance, taken in connexion with the fact that the fibres pursue a very 
oblique direction, has given rise to the belief that the fibres of the sphincter and neck 
of the bladder generally are circular fibres, which is not the case. The fibres of the 
sphincter are best seen by inverting the bladder and dissecting from within, or by 
making transverse sections of the prostatic portion of the urethra in the direction of the 
fundus (Plate IV. figs. 19 & 20, to). They are most strongly pronounced at the cervix, 
but are continued forward on the urethra, and backwards into the bladder. In the 
female they extend even to the meatus urinarius. The apex and base of the bladder 
are similarly constructed, and resemble in their general configuration the other por- 
tions of the vesical walls ; i. e. they are composed of longitudinal or vertical, slightly 
oblique, oblique, and very oblique spiral fibres, which cross in all directions externally 
and internally (Plate IV. figs. 13, 14 & 15). The longitudinal or vertical, slightly 
oblique, oblique, and very oblique external and internal fibres at the base are continued 
forwards within the prostate to the membranous portion of the urethra and the external 
and internal surfaces of the corpus spongiosum ( vide Cervices of figs. 1, 4 & 7, Plate III.). 
The coats of the urethra are therefore to be regarded as the proper continuation of the 
walls of the bladder in an anterior direction. The external or longitudinal, slightly 
oblique, oblique, and very oblique spiral fibres which form the three outer and the 
central or circular tunic of the bladder and urethra, are curiously enough repeated in 
the prostate of the male and the analogous structure in the female, so that this gland 
would seem to be composed chiefly of fibrous offsets from the longitudinal, slightly 
oblique, oblique, and very oblique or circular fibres in question. To understand the 
relations existing between the bladder, prostate, and urethra, it will be most convenient 
to regard the four outer layers of the bladder as splitting up at the neck of the viscus, 
* The right and left lateral walls are strengthened by the plexuses of blood-vessels and nerves, and by the 
cellular and fibrous tissues which abound in these situations. 
