30 
DR. PETTIGREW ON THE MUSCULAR ARRANGEMENTS 
selves to the right and left sides respectively. They converge at the cervix to assist in 
forming the sphincter, as explained. 
Fourth , or central layer , consisting of fibres arranged in figure-of-eight loops , crushed 
together to produce the maximum of lateral distention. — Returning, for a fourth time, 
to the anterior aspect, we discover a still deeper and more oblique set of fibres. These, 
like their predecessors, form figure-of-eight loops; the loops in this instance being flattened 
from above downwards, and from below upwards. Proceeding with the description as 
before, we trace the fibres from the left of the posterior median line round upon the 
left side (Plate III. fig. 1 ,k), then on the anterior aspect, then on the right side (/), and 
onward to the posterior of the cervix, where they reverse their course to proceed in an 
upward and very oblique spiral direction (to n). They ultimately reach the point from 
which they started, and in this way become continuous at the apex and base. Their 
course is indicated at Plate V. diag. 1, Jclmn. These fibres spread out on the lower 
two thirds of the bladder posteriorly, and form a layer of great thickness. They thus 
complete, by their flattened terminal loops, the lower portion of the so-called circular 
layer on this aspect (Plate III. fig. 5, y z; fig. 12, Jc l). They converge on the sides, and 
on reaching the anterior mesial line at a point half an inch or so above the cervix, are 
plainly seen to cross each other. On the posterior aspect of the cervix they are crowded 
together, and are principally concerned in forming the posterior lip op the sphincter 
vesicle (Plate III. fig. 4 ,yy', zz' \ Plate V. diagram 4, zzz, y' y' y'). Many of them are 
prolonged on the ventral aspect of the urethra (Plate III. fig. 9, to), especially its pro- 
static portion, while others proceed to the prostate itself (Plate V. diag. 8, g g'). Turning 
to the posterior aspect, a corresponding set of fibres is met with (Plate V. fig. 4 ,yy', z z'). 
These fibres come from the mesial line anteriorly, and curve round on the left side in a 
downward and very oblique spiral direction until they reach the mesial line posteriorly. 
They then proceed to the right, and curve round the cervix anteriorly, so as to change 
their course, and return in an opposite and upward direction to where we began to 
trace them. These fibres are greatly developed, and in their turn spread out on the 
lower two thirds of the anterior aspect, to complete what was wanting of the circular 
layer in this direction (Plate III. fig. 3, Jc l). They converge at the apex anteriorly, and 
are largely concerned in the formation of the anterior lip op the sphincter (Plate III. 
fig. 1, Jclmn; Plate V. diagram 2, to to/ to", 1 1' l"). Many of them are continued for- 
wards on the dorsum of the urethra, and form, with corresponding fibres found on the 
ventral aspect, the so-called circular layer of the prostatic and membranous portions of 
the urethra. The lower portions of the bladder, the sphincter, and the prostatic and 
membranous portions of the urethra are thus plainly bilateral. 
Two sets of similar, though less fully developed fibres occur on the sides of the bladder 
(Plate III. fig. 9, to n), and contribute to the formation of the lower portion of the central 
layer, sphincter, and urethral canal in these directions. It will be evident from this 
description that the so-called central or circular layer is not composed of circular fibres 
having a uniform direction, as figured by Sabatier, Ellis, and others, but of very oblique 
