OE THE BLADDER AND PROSTATE, 
25 
In the Koala no posterior ridge can be discerned, but the remaining three, viz. the ante- 
rior and two lateral (Plate IV. fig. 34, op, s t), are strongly pronounced. In the human 
and other bilateral bladders (to which my subsequent remarks more particularly apply) 
two ridges alone persist, viz. the anterior (Plate III. fig. 1, a b) and posterior (Plate III. 
fig. 6, o ). They correspond with what has been described as the great anterior and pos- 
terior longitudinal bands of fibres, and during the distended state of the viscus have their 
height so greatly reduced by lateral stretching as scarcely any longer to deserve the 
name of ridges. They, however, have their homologues in bladders of a lower type, and 
occasion a thickening of the wall of the bladder anteriorly and posteriorly which cannot 
otherwise be easily accounted for. It is a curious fact, and not without interest as far 
as the comparative anatomy of the bladder is concerned, that traces of the fourfold ar- 
rangement alluded to above may not unfrequently be detected in the human bladder, 
particularly at the apex and base. In one specimen which I dissected and preserved, it 
is especially distinct (Plate IV. fig. 16, ao, kl; fig. 18, bp, mn). 
Although it is usual to speak of the fibres constituting the muscular coats of the 
bladder as longitudinal and circular, it may be as well to state that, strictly speaking, 
those terms are inapplicable, the so-called longitudinal fibres for the most part curving 
and diverging either in an antero-posterior or lateral direction, and the circular ones 
representing the aggregate of terminal loops, or very oblique fibres crossing at very ob- 
tuse angles. The terms therefore have been retained in the text rather with a view to 
assimilating my description with that of previous writers, and because it is convenient to 
have an ideal standard of comparison than because of their correctness. The best 
standard by which to compare the direction of the fibres is a line drawn from the cervix 
of the bladder anteriorly to the urachus and cervix posteriorly, another being made to 
extend from the right side of the cervix to the urachus and left side. A third line may be 
drawn transversely, or at right angles to both. 
It has likewise been customary to regard the fibres constituting the vesical parietes as 
consisting of layers, but here, again, it is necessary to explain that the strata of the ana- 
tomist find no exact counterpart in the bladder itself, the fibres rarely, if ever, occupy- 
ing precisely the same plane and running exactly parallel. They moreover split up and 
become fused with each other, with corresponding or homologous fibres, and with fibres 
which are either superimposed or underlie them. The term layer, which has also been 
retained, is consequently used in a restricted sense. 
In the subjoined account I make no distinction between the male and female bladder, 
the difference which exists between the two referring rather to shape and to the greater 
length of the urethra in the former than to the general arrangement of the fibres them- 
selves. I have, moreover, taken my description from young and adult normal bladders, 
from a feeling that Bell, Sabatiek, and other investigators have given undue prominence 
to certain fibres or sets of fibres from having dissected abnormally thickened or hyper- 
trophied bladders. As mere verbal descriptions, however voluminous and precise, would 
fail to convey an adequate conception of the various combinations formed by the fibres 
mdccclxvii. e 
