28 
DE, PETTIGEEW ON THE MUSCITLAE AEEANGEMENTS 
view. They reappear on the anterior surface, recross the anterior mesial line, and wind 
round in an upward spiral direction until they reach the right of the mesial line pos- 
teriorly, where we began to trace them. Their course is given in Plate V. diagram 
1, ghij. 
The fibres under consideration form a broad expansion on the upper third of the 
bladder posteriorly (Plate III. fig. 7, g). On the sides and anterior aspect ( g d) they con- 
verge until they reach the anterior mesial line, where they cross each other, after which 
they again slightly expand in a backward direction to assist in forming the posterior 
half of the sphincter vesicse (Plate III. fig. 4, vw). They constitute a patch or layer of 
considerable thickness. Their direction at the upper third of the bladder posteriorly, 
and at the posterior aspect of the cervix, is nearly transverse, owing to the large curves 
made by the terminal portions of the loops. In those situations they form, with inci- 
dental or accessory fibres which are developed between them, part of the so-called 
transverse or circular layer of the older anatomists. Turning to the posterior sur- 
face, a similar disposition of the fibres can be made out. Here, however, owing, as 
has been already explained, to the greater posterior measurement of the bladder, the 
looped arrangement is not so obvious (Plate III. figs. 4 & 6, uvwx). That the fibres 
diverge from the mesial line in an upward direction is at once apparent, but that they 
cross and diverge in a downward direction is not so evident. Sabatier* was of opi- 
nion that they did not cross, and has represented them as coming together and sepa- 
rating as in the italic letter x . The crossing, however, as I have abundantly satis- 
fied myself, does occur. Its site corresponds to a point in the mesial line about two 
inches above the base of the prostate. 
The external fibres forming the third layer or patch posteriorly may be briefly 
described. They proceed from the left of the mesial line anteriorly, and curve in a 
downward and backward spiral direction until they reach the point indicated. Con- 
tinuing their downward course, they cross the median line posteriorly, and curve round 
on the cervix anteriorly, where they assist in forming the anterior half of the sphincter 
vesicse (Plate III. fig. 1, li i). They reappear on the posterior surface, recross the posterior 
median line, and curve in an upward and forward spiral direction until they reach the 
right of the median line anteriorly whence they set out. Their course is traced in 
Plate V . diagram 3, uvwx. 
The posterior fibres of the third layer in this manner form figure-of-eight loops like the 
anterior ones ; the loops of either set being so arranged that the terminal portions of 
each appear either on the anterior or posterior surface. They are continued forwards 
upon the dorsal and ventral surfaces of the urethra (Plate V. diagram 8. 3 ), and like- 
wise upon the dorsal and ventral surfaces of the prostate (3'). This disposition of the 
fibres imparts a highly symmetrical appearance to the bladder, the terminal loops being 
arranged in two sets at the apex (Plate IV. fig. 15) and cervix (fig. 17), rendering it 
strikingly bilateral in these directions. I am axious to be explicit on this point, as it 
* Op. cit. 
