OF THE BLADDER AND PROSTATE. 
31 
spiral fibres crossing at very obtuse angles, mixed up with the greatly expanded 
terminal portions of the loops forming the several layers. It ought, however, to be 
mentioned that a certain number of incidental or accessory fibres is developed between 
the crossings formed by the very oblique fibres which confer upon the layer a certain 
degree of uniformity. The layer in question is seen anteriorly at Plate III. figs. 3 & 11, 
■k l, posteriorly at figs. 5 & 12, y z' k l, and laterally at fig 9, m n. It is traced in 
outline at Plate V. diagram 2 , k n, m l ; diagram 4, yz\ diagram 6, kn, ml , and 
diagram 10, y l. The fibres forming the great central layer are united to each other 
where they intersect ; they also interchange fibres with the layers to the outside and 
inside of them. 
INTEENAL FIBEES. 
Comprising layers 5, 6, and 7 ( imperfect ). — If the central layer be removed, which, 
owing to its great thickness and the tenuity of the internal fibres, is a matter of 
difficulty, it will be seen that the fibres to the inside of it, or the internal fibres proper, 
are arranged very much in the same way as the external fibres already described. The 
internal fibres are best seen when the bladder is inverted and the dissection conducted 
from within. They are, as compared with the external fibres, rudimentary and 
scantily developed. They do not, however, pursue the simply longitudinal course 
usually attributed to them. On the contrary, their direction is varied as in the 
external fibres. Thus those occurring in the mesial line anteriorly (Plate III. fig. 10, a b) 
and posteriorly (fig. 12, oo,pp ) are more or less vertical, while those to the outside of 
them or nearer the central layer, diverge from the line in question, and show a decided 
tendency to the looped arrangement (Plate III. fig. 10, c d ef) ; those still deeper making 
unmistakeable spiral curves ( ghij ) analogous to those made by corresponding external 
fibres. The same remarks, if allowance be made for their more fragmentary condition, 
may be made regarding the course and distribution of the internal fibres occurring on 
the sides of the bladder. The various sets of internal fibres cross each other like the 
external ones, the more longitudinal fibres at acute angles, the more circular or deeper 
ones at obtuse angles. They are continued on the ureters and urethra, and in the 
latter situation, owing to the smaller space occupied by them, are more plentiful (Plate 
III. fig. 10, b). Their general distribution in the interior of the urethra is given in the 
section headed trigone further on. The internal fibres of the bladder in some instances 
are so straggling that they form a network of large meshes. They are united by 
accessory slips to corresponding external ones, and the external in some instances 
originate the internal as in the heart. The internal fibres are so delicate in com- 
parison with the fibres of the great central layer (Plate III. fig. 12, kl), that in the 
hypertrophied bladder the circular ones tear them asunder so that they partially 
or altogether disappear. 
Distribution of the external and internal fibres at the apex and fundus. — The various 
directions pursued by the external and internal fibres on the walls of the bladder 
generally are readily made out at the apex and fundus, both from without and from 
