( 770 ) 
lie outside each other (see fig. 1). Then we can join tr, and ty by 
an are of simple curve (drawn splintered in the figure), which lies 
inside as well as inside the domain enclosed between p and the 
image skeleton are 9,77,,419-41, and which we shall call the path 
Fig. 1. 
arc aj. This path are together with the image skeleton are 
Tt does not separate the skeleton arc PP from tbe infinite. 
So, if we represent by y, the total angle described by a vector of 
which the origin runs along the skeleton are PP, and the end- 
point as a continuous function of the origin along the path are 
TT, we have is this first case: 
Bi = Yk 
21, On the circumference of p the segment ReRpya is a part of 
the segment 9.0.41. Then too we can construct a path are Tt 
(drawn splintered in fig. 2), which lies inside } as well as inside 
the domain enclosed between g and the image skeleton arc 
Fig. 2. 
OTTO. But now this path are forms with the image skeleton 
arc Tite a simple closed curve containing the skeleton arc PiP 
in its inner domain, whilst its positive sense of circuit corresponds to 
a movement from t, to t%41 along the image skeleton are tz tj. 
