206 
plete ring of muscle around the duct. This arrangement must not, 
however, be regarded as perfectly symmetrical. Furthermore, some 
sections in this region show a simple decussation of fibres of the upper 
division with fibres of the lower division of the inner circular muscular 
coat. This latter arrangement (decussation on both sides of the common 
bile-duct) seems to hold entirely for the second set of serial sections. 
On both sides of the lumen of the common bile-duct, muscle bundles 
in transverse section are seen. These represent those bundles of muscle 
which have origin in the median line of the common bile-duct and 
afterwards run forward parallel with the long axis of the tube (see N). 
er 
0000004 Ul 
0 
> 08900 M 
MAW AI W 
OR 744 nn 
ee ILO, 
2 ZB —E SEINE OO 
N IE 
III = & 
~ INN 
SRG 
DANY oO & 
WY N I —Mı 
MW) NS OD 
N 
NUN ae ae © 6 
\ 
5 
4 FMA Wt Wy 
Ir Sanh 
Fig. 7. Cross-section somewhat removed from the middle of the duodenal portion 
of the common bile-duct of dog. X 30. 
Fig. 7 shows those muscle bundles which arise in the median line 
of the common bile-duct. They are seen here only on the right 
running down over the side of the bile-duct, N; it should be noted, 
however, that this arrangement is bilateral. The bundles of muscle 
cut transversely represent those muscle bundles which run forward, 
parallel with the common bile-duct, after taking their origin in the 
median line of the bile-duct. 
Fig. 8 is taken at a point where the bile-duct has almost left 
the intestinal wall. The inner circular muscular coat passes entirely 
over the common bile-duct at this point. At the sides are seen large 
masses of longitudinal muscle fibres. These are the fibres of the 
