208 
continuous with the fibres of the inner circular muscular coat. The 
presence of some fibres of the inner circular muscular coat just under 
the ampulla of VATER is to be noted, CS. 
Fig. 9 also shows a sphincter muscle about the orifice of the 
common bile-duct, S. This sphincter is composed of a muscular 
ring which surrounds the orifice of the duct. Some fibres instead of 
running completely around the orifice, run off at the side of the ring 
and bending forward become continuous with the fibres of the inner 
circular muscular coat. 
The fibres of the inner circular muscular coat were next removed 
(except at CS). The arrangement seen is represented in Fig. 10. 
The common bile-duct is seen penetrating the outer longitudinal mus- 
cular coat. The outer longitudinal muscle at the point of entrance of 
the common bile-duct, A, covers some muscle fibres which run around 
the common bile-duct embracing it. Immediately after penetrating 
the outer longitudinal muscular coat, the bile-duct can be seen to be 
encircled with smooth muscle. Those muscle fibres nearest the point 
of entrance of the common bile-duct, run around or encircle the bile- 
duct without bending forward, IR, but as the orifice of the duct is 
approached the muscle fibres which embrace the bile-duct, after run- 
ning down over the side of the duct, bend forward more and more. 
Fig. 10. Macerated duodenal portion of 
the common bile-duct of rabbit. The greater 
part of the circular muscular coat of the in- 
testine has been removed. 4. 
Fig. 11. Macerated duodenal portion of 
the common bile-duct of rabbit, showing the 
distribution of the CS and JR fibres, X 4. 
A a) 
Fig. 10. Fig. 11. 
Thus it will be seen that in all cases, the muscle fibres described 
embrace the duct but with the difference pointed out above, namely, 
that those fibres nearest the point of entrance of the common bile- 
duct do not bend forward as they pass under the common bile-duct, 
while those nearer the orifice of the bile-duct do bend forward as 
they pass under it. All the muscle fibres just mentioned doubtless 
have a sphincter function, but if we regard the sphincter muscle of 
the dog we will find it homologous with the sphincter fibres, S, of 
the rabbit. Therefore, the rabbit has not only a sphincter similar to 
that of the dog, but it possesses also other fibres which subserve in 
all probability the same or a similar function. 
