32 
DE. PETTIGREW ON THE MUSCULAR ARRANGEMENTS 
within. In fact if a cylinder composed of external and internal longitudinal slightly 
oblique, oblique, and very oblique fibres be constricted at either end, the general scheme 
of the arrangement of the fibres at the summit and base is at once apparent. The 
longitudinal or vertical fibres, particularly the external ones, bend over and unite, to 
form a crucial arrangement, the anterior joining with the posterior and the lateral with 
each other (Plate IV. fig. 16, ao,/cl; fig. 18, bp, mn). The slightly oblique and' 
oblique fibres in like manner bend over and unite, those because of their obliquity 
occasioning a stellate arrangement, which causes at the apex a corresponding thickening 
of the wall (Plate IY. figs. 13 & 15, x), and at the cervix a thickening and funnel-shaped 
puckering, which largely contributes to the closure of the urethral orifice (Plate IV. figs. 
14 & 17, 2 , 2 ). The very oblique fibres, because of the greater size of the loops formed 
by their junction, furnish what are known as the circular fibres, and are continued on 
the body of the viscus generally (Plate IV. figs. 13, 15, & 16, Jc l, and figs. 14, 17 & 18, 
m n ). The circular fibres, which are plentifully developed at the cervix, where they 
contribute largely to the formation of the sphincter, occur to the outside of the 
internal stellate fibres, and, with the elasticity natural to the parts, are principally 
concerned in the closure of the urethral orifice. This orifice, it may be remarked, is as 
impervious as the urachus itself when the urine is not actually passing through it, a 
considerable degree of pressure being necessary, even in the dead bladder, to force a 
passage. As might be supposed from this explanation, the apex and base, if allowance 
be made for the apertures of the ureters and urethra and the expanded condition of the 
viscus in the latter direction, are structurally identical. This is particularly evident 
when the apex and base are rendered transparent, and compared by being held against 
the light. When viewed from within, the various sets of vertical, slightly oblique, 
oblique, and very oblique fibres can be made out without difficulty. The crossing of 
the oblique and very oblique fibres concerned in the formation of the central layer is 
especially evident. These fibres, in conjunction with the accessory fibres developed 
between them, form tolerably perfect circles or rings, which invest the summit and base, 
particularly that portion of the base which corresponds with the cervix (Plate IV. fig. 17, 
22 ). I draw attention to this arrangement because of the symmetry it everywhere 
secures, and because in no work with which I am acquainted has the arrangement of the 
fibres at the apex and base been either described or figured. The fibres in question are 
shown at Plate IV. figs. 13, 14, 15, 16, 17 & 18, 
TKIGOEE. 
Uvula , venimontanum ; ureters and urethra — closure of \ &c . — The only points re- 
quiring further elucidation pertain to the ureters and urethra, and that triangular space 
which occurs between them familiarly known as the trigone (Plate V. diagram 7, 
z v s ). The space referred to has received a large share of attention, partly on account of 
its surgical importance, and partly because many authors suppose that the fibres and tissues 
composing it are specially constructed, and have particular functions assigned to them. 
