24 
DR. PETTIGREW ON THE MUSCULAR ARRANGEMENTS 
the urethra, but they have, as was shown by Sabatier, separate axes — the circular fibres 
of the urethra being concentric to the canal of the urethra, and eccentric to the circular 
fibres of the prostate (Plate IV. fig. 24, m, o ). The only fibres which can with accuracy 
be regarded as continuous with the circular fibres of the bladder, are the corresponding 
fibres of the urethra (Plate III. fig. 9, m, n). The various sets of fibres in the vesical 
parietes are elaborately interlaced, the most external or superficial ones being connected 
directly and indirectly with the slightly oblique external, the slightly oblique external 
with the oblique external, and the oblique external with the very oblique or central fibres. 
The very oblique internal fibres, on the other hand, are connected with the oblique internal, 
these in their turn being connected with the slightly oblique internal, and the slightly 
oblique internal with the longitudinal or vertical internal. In some instances the longi- 
tudinal external are connected directly with the longitudinal internal, and so of the slightly 
oblique, oblique, and very oblique external and internal fibres. The bladder, urethra, and 
prostate are bilaterally symmetrical, and the fibres composing them pursue something like 
seven directions, the fibres crossing with remarkable precision at wider and wider vertical 
angles as the centre of either is reached, as in the stomach and heart *. In fact the 
fibres of the bladder, stomach, and heart have a strictly analogous arrangement, and I am 
inclined to believe that functionally also they possess points of resemblance. Very similar 
remarks may be made regarding the structure and functions of the uterus. 
From a careful examination of a large number of mammalian bladders, I am of opi- 
nion that fundamentally the fibres are arranged in two principal directions, viz. vertically 
or longitudinally (Plate IV. fig. 34 & 36, s ), and transversely or circularly (m). In the 
primary or typical bladder the vertical fibres, particularly in the undistended condition, 
are grouped together, and form ridges which are raised considerably above the level of 
the transverse fibres. The ridges, two in number, run from the urethra anteriorly to 
the urachus and urethra posteriorly, and from side to side. The former bisects the 
bladder in an antero-posterior direction, the other laterally. As the urachus naturally 
disconnects the ridges at the apex of the bladder, they may be conveniently described 
as the anterior, posterior, and right and left lateral ridges. They are seen to advantage 
in the bladders of the Ox (Plate IY. fig. 36, a b, op, s ), Cat (Plate IY. fig. 38, a V, c d, op), 
Sheep, Roebuck, and Wombat, and map out the circular fibres into four distinct regions. 
The fibres constituting them are united to the circular ones by short oblique fibres (Plate 
IV. fig. 36, m), and it may be stated that the so-called longitudinal and circular fibres 
are, with few exceptions, the most strongly marked. This is precisely what we should 
expect if, as Baer and Rathke affirm, the bladder is formed originally from the intes- 
tinal tube. The ridges are not always persistent, and the disappearance of a ridge ne- 
cessitates a higher degree of differentiation in the fibres themselves, i. e. it demands an 
increase in the number of oblique fibres. In the Ox, Sheep, and Pig the lateral ridges 
are but feebly developed, and in the Horse the posterior one has all but disappeared. 
* See paper by the author “ On the Arrangement of the Muscular Fibres in the Yentricles of the Yertebrate 
Heart,” Phil. Trans. Part III. 1864. 
